Key Takeaways
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Shallower needles (0.6mm) outperformed deeper needles (1.2mm) — this randomised controlled trial found that 0.6mm microneedling combined with minoxidil produced greater improvements in both hair count and hair thickness than 1.2mm needling.
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Both microneedling depths beat minoxidil alone — adding microneedling at either depth significantly improved results compared to minoxidil 5% used on its own, confirming the value of combining these treatments.
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0.6mm achieved stronger statistical significance — the shallower depth produced improvements in hair count (P = 0.017) and thickness (P = 0.007) versus controls, with the deeper depth showing significant investigator-assessed improvement (P = 0.04) but less impressive quantitative measures.
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Less pain with shallower needles — patients in the 1.2mm group reported significantly more pain during treatment than those in the 0.6mm group, making the shallower depth more comfortable while also being more effective.
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This directly supports at-home microneedling protocols — the finding that 0.6mm is effective (and potentially superior to deeper needling) validates at-home derma roller depths, which typically range from 0.25mm to 1.0mm.
Evidence at a Glance
| Evidence Level |
Level 2b — Randomised controlled trial (3 groups) |
| Sample Size |
60 patients randomised (59 completed: 29 male, 30 female) |
| Key Result |
0.6mm depth significantly improved hair count (P = 0.017) and thickness (P = 0.007) vs minoxidil alone |
| Treatment Duration |
12 weeks (6 biweekly microneedling sessions) |
| Needle Depths |
0.6mm vs 1.2mm vs minoxidil-only control |
| Safety |
More pain with 1.2mm; no serious adverse events at either depth |
About This Study
| Authors |
Gita Faghihi, Samin Nabavinejad, Fatemeh Mokhtari, Farahnaz Fatemi Naeini, Fariba Iraji |
| Journal |
Journal of Cosmetic Dermatology |
| Year |
2021 (published April) |
| Volume/Pages |
Vol. 20, Issue 4, pp. 1241–1247 |
| Type |
Randomised controlled trial |
| PMID |
32897622 |
| DOI |
10.1111/jocd.13714 |
| Institution |
Isfahan University of Medical Sciences, Iran |
| Full Paper |
View on PubMed → |
Note: This is a plain-language summary of the published research paper. The original study was conducted independently and is not affiliated with Hairgenetix. We present this summary to make scientific research more accessible to people experiencing hair loss.
Reviewed by: Esther Bodde, MSc — Health Scientist and Medical Research Analyst at Hairgenetix. Esther holds a Master of Science degree and specialises in translating clinical research into clear, evidence-based consumer information. This summary was reviewed for scientific accuracy, fair representation of results, and clear communication of study limitations.
Why This Research Matters
By 2021, multiple studies had confirmed that microneedling improves hair growth outcomes when combined with topical treatments. But a critical practical question remained unanswered: how deep should the needles go? Is deeper better — reaching closer to the hair follicle bulb — or is shallower sufficient?
This matters enormously for patients using at-home microneedling devices. Deeper needles (1.0mm+) are more painful, carry higher risk of adverse effects, and are generally recommended only under professional supervision. If shallower depths (0.5–0.6mm) achieve equal or better results, it means effective microneedling is safely achievable at home with standard derma rollers — no clinic visits required.
Faghihi and colleagues designed a head-to-head comparison to answer this question directly. Their finding — that 0.6mm produced better quantitative results than 1.2mm while causing less pain — has significant practical implications for anyone incorporating microneedling into their hair loss regimen.
This finding is also corroborated by the Xu 2024 meta-analysis, which found in its subgroup analysis that needle depths below 1mm produced larger effect sizes (SMD 1.16) than depths above 1mm (SMD 0.52) — strengthening the evidence that shallower is often better.
What The Researchers Did
Faghihi and colleagues recruited 60 patients (29 men and 30 women, aged 18–45) with moderate to severe androgenetic alopecia and randomly assigned them to three groups:
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Control group: Topical minoxidil 5% lotion applied daily — the standard treatment, used alone without microneedling.
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Group A (1.2mm): Topical minoxidil 5% daily plus biweekly microneedling sessions using an automated dermapen at 1.2mm needle depth.
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Group B (0.6mm): Topical minoxidil 5% daily plus biweekly microneedling sessions using the same automated dermapen at 0.6mm needle depth.
All microneedling sessions were performed every two weeks for 12 weeks (6 sessions total). The treatment endpoint for each session was pinpoint bleeding — the appearance of tiny blood droplets on the scalp surface, indicating the needles have reached the dermis and triggered the wound-healing response.
Results were assessed using four outcome measures:
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Hair count: The number of hairs in a standardised target area, measured before and after treatment
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Hair diameter: The thickness of individual hair shafts, measured microscopically
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Investigator assessment: Blinded evaluation of photographic improvement by the research team
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Patient self-assessment: The patient's own perception of improvement
Understanding the Research Methods
Why a three-group design? By including both a control group (minoxidil only) and two treatment groups (different needle depths), the researchers could answer two questions simultaneously: (1) Does adding microneedling to minoxidil improve results? (2) Does needle depth matter? This is more efficient and informative than running two separate two-group studies.
What is pinpoint bleeding and why is it the endpoint? Pinpoint bleeding — tiny droplets of blood appearing on the scalp surface — indicates that the needles have penetrated through the epidermis into the dermis, where blood vessels and hair follicle structures reside. This confirms adequate penetration depth and triggers the wound-healing cascade that releases growth factors. Using pinpoint bleeding as the session endpoint ensures consistent treatment delivery regardless of individual differences in skin thickness.
Why use an automated dermapen? Unlike manual derma rollers, an automated dermapen (pen-style device) delivers vertical needle insertions at a consistent depth, speed, and angle. This reduces variability between sessions and patients, making the comparison between depths more scientifically valid. The vertical insertion is also less traumatic to tissue than the rolling motion of a derma roller.
Why include both men and women? With 29 men and 30 women, the study evaluated microneedling across both populations — important because most microneedling research has focused on men. Including both sexes increases the generalisability of the findings.
What They Found
0.6mm significantly improved hair count over minoxidil alone: The shallower microneedling group (0.6mm) demonstrated a statistically significant increase in total hair count compared to the minoxidil-only control group (P = 0.017). This confirms that even at a relatively shallow depth, microneedling adds meaningful benefit to topical treatment.
0.6mm significantly improved hair thickness: Hair shaft diameter in the 0.6mm group increased significantly compared to controls (P = 0.007). This is noteworthy because some meta-analyses (Abdi 2023, Xu 2024) found that microneedling's effect on hair diameter was borderline or non-significant — yet this individual trial detected a clear effect at the shallower depth.
Both depths showed investigator-assessed improvement: Blinded investigator evaluation of photographic results favoured both microneedling groups over controls — Group A (1.2mm) at P = 0.04 and Group B (0.6mm) at P = 0.007. The shallower depth actually achieved a stronger level of statistical significance.
0.6mm tended to outperform 1.2mm: In the quantitative measures of hair count and thickness, the 0.6mm group showed greater changes than the 1.2mm group. While the direct comparison between the two microneedling groups may not have reached statistical significance (the study was powered for treatment vs control comparisons), the trend consistently favoured the shallower depth.
Less pain with 0.6mm: Patients in the 1.2mm group reported significantly more pain during microneedling sessions than those in the 0.6mm group. Given that the shallower depth also produced better quantitative results, this finding offers the ideal combination: more effective and more comfortable.
All groups improved over baseline: A significant increase in hair count and hair thickness was observed across all three groups (P < 0.05), including the minoxidil-only control. This confirms that minoxidil works on its own, but adding microneedling — particularly at 0.6mm — produces significantly greater improvement.
Figure 1: Summary of findings from Faghihi et al. (2021). Left: statistical significance of each microneedling depth compared to minoxidil-only controls. Centre: three-group study design showing treatment arms. Right: practical implications of the depth comparison for at-home microneedling. Data source: J Cosmet Dermatol 2021;20(4):1241-1247.
Why Shallower Needles May Work Better: The Biological Explanation
The dermal papilla sweet spot: Hair follicle stem cells and the dermal papilla (the command centre of the follicle) reside in the upper-to-mid dermis, approximately 1–2mm below the scalp surface. However, the growth factor–rich zone — where wound-healing signals trigger follicle stimulation — begins at the junction of the epidermis and dermis, just 0.3–0.6mm deep. A 0.6mm needle reaches this critical zone effectively.
Inflammation balance: Microneedling works through a controlled wound-healing response. Too little penetration doesn't trigger enough growth factor release. But too much penetration can cause excessive inflammation — and chronic or excessive inflammation is actually harmful to hair follicles, potentially pushing them into the catagen (regression) phase. The 0.6mm depth may hit the "sweet spot" of sufficient growth factor stimulation with minimal damaging inflammation.
Micro-channel depth and topical absorption: Microneedling creates temporary channels that allow topical products to penetrate more deeply. Research shows that even relatively shallow channels (0.25–0.5mm) dramatically increase the absorption of topically applied ingredients. The 0.6mm depth creates channels that extend well into the dermis — sufficient for excellent product delivery — without the additional tissue damage of deeper penetration.
Wnt signalling activation: The wound-healing cascade triggered by microneedling activates the Wnt/β-catenin signalling pathway — essential for hair follicle cycling and neogenesis. This pathway activation appears to be triggered effectively at shallower depths, as the relevant stem cell populations are located in the upper follicle region (the bulge area) rather than deep in the dermis.
Clinical Interpretation
This study provides one of the few direct, head-to-head comparisons of microneedling depths for hair loss. Several aspects of the findings deserve careful consideration:
The counterintuitive result makes biological sense: Many people assume "deeper = better" for microneedling. This study challenges that assumption with data showing the opposite trend. The biological explanation — that the relevant targets are in the upper dermis and excessive depth causes counter-productive inflammation — aligns with the findings and with the Xu 2024 meta-analysis subgroup analysis.
Both depths work: It's important to note that both 0.6mm and 1.2mm produced improvements over minoxidil alone. The question isn't whether deeper needles work — they do — but whether the additional depth provides additional benefit. The answer from this trial is no; the additional depth appears to provide no advantage and may actually slightly reduce the treatment effect while increasing pain.
Sample size considerations: With approximately 20 patients per group, this study has moderate statistical power. The fact that significant differences were detected despite the modest sample size suggests the treatment effects are genuinely meaningful. However, the study may have been underpowered to detect a statistically significant difference between the two microneedling depths in a direct comparison.
Corroboration from meta-analyses: The Xu 2024 meta-analysis independently confirmed this pattern: in their subgroup analysis, needle depths below 1mm produced a standardised mean difference of 1.16 versus 0.52 for depths above 1mm. The convergence of evidence from both individual trials and pooled analyses strengthens the conclusion.
How This Compares With Other Research
| Study |
Needle Depth |
Subjects |
Key Finding |
| Faghihi 2021 (this study) |
0.6mm vs 1.2mm |
60 patients (RCT) |
0.6mm better than 1.2mm for hair count and thickness |
| Dhurat 2013 |
1.5mm |
100 men |
+91.4 hairs/cm² vs +22.2 with minoxidil alone |
| Xu 2024 (meta-analysis) |
Subgroup: <1mm vs >1mm |
8 RCTs, 472 patients |
SMD 1.16 for <1mm vs 0.52 for >1mm (shallower better) |
| Abdi 2023 (meta-analysis) |
Mixed (0.5–2.5mm) |
10 RCTs, 466 patients |
SMD 1.76 overall (P < 0.00001) for combination |
The Dhurat 2013 landmark study used 1.5mm needles and achieved dramatic results. However, that study used weekly sessions (higher frequency than Faghihi's biweekly) and did not include a shallower-depth comparator. The Xu 2024 meta-analysis subgroup data aligns with Faghihi's finding, suggesting that the dramatic results in the Dhurat study may have been driven more by the weekly frequency than by the specific 1.5mm depth.
Treatment Protocol Details
| Device |
Automated dermapen (pen-style microneedling device) |
| Needle Depths Tested |
0.6mm (Group B) and 1.2mm (Group A) |
| Session Frequency |
Biweekly (once every 2 weeks) |
| Total Sessions |
6 sessions over 12 weeks |
| Session Endpoint |
Pinpoint bleeding (tiny blood droplets confirming dermal penetration) |
| Concurrent Treatment |
Topical minoxidil 5% lotion applied daily in all groups |
| Patient Population |
Ages 18–45 with moderate to severe androgenetic alopecia (both sexes) |
At-home adaptation: The 0.6mm depth used in this study is within the range achievable with at-home derma rollers (0.25mm to 1.0mm). Most dermatologists recommend 0.5mm to 1.0mm for at-home use, with sessions once weekly to once every two weeks. The key is consistency — maintaining a regular schedule over at least 12 weeks — rather than using aggressive depth or frequency.
Research Limitations to Consider
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Modest sample size: With approximately 20 patients per group, the study provides meaningful evidence but limited statistical power for detecting smaller differences, particularly in the direct comparison between the two needle depths.
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Low quality score: A systematic review rated this study with a Jadad score of 2 out of 5, indicating limitations in methodological reporting such as blinding description and randomisation details.
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Short duration: The 12-week treatment period captures early treatment response but doesn't establish long-term outcomes. Hair biology operates on longer timescales — the full growth cycle takes 2–6 years — so longer follow-up would provide a more complete picture.
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Single centre: The study was conducted at one institution in Isfahan, Iran, which may limit generalisability to different populations, environmental conditions, or genetic backgrounds.
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Dermapen vs derma roller: The study used an automated dermapen, which delivers vertical needle insertions. Results may not directly translate to manual derma rollers, which create angled punctures with a rolling motion. However, both devices achieve the same fundamental goals of micro-channel creation and growth factor stimulation.
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No longer-term follow-up: The study doesn't tell us whether the 0.6mm advantage persists with continued treatment, or whether the optimal depth might shift over time as follicles respond.
What This Means For Your Hair
This study directly addresses one of the most common questions people ask about microneedling for hair loss: how deep should the needles be? The answer — supported by this trial and corroborated by the Xu 2024 meta-analysis — is encouraging for anyone using at-home devices:
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You don't need to go deep to get results: The 0.6mm depth produced statistically significant improvements in both hair count and hair thickness. This depth is comfortably within the range of standard at-home derma rollers (typically 0.25mm to 1.0mm), meaning you can achieve clinically meaningful results without clinic visits or aggressive needling.
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Shallower means less pain: Patients using 0.6mm needles experienced significantly less pain than those using 1.2mm. Since consistency is the most important factor in any hair loss treatment, a protocol that's comfortable enough to maintain over months and years has a real advantage over one that's painful to endure.
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The 0.5mm Hairgenetix derma roller aligns with this evidence: The derma roller depths commonly recommended for at-home hair loss treatment (0.5mm to 1.0mm) fall squarely in the range that this study and the Xu meta-analysis found to be most effective. You're not compromising on results by choosing comfort — the evidence suggests you may actually be optimising them.
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Combine with topical treatment for best results: All groups in this study used minoxidil as a baseline. The micro-channels created by microneedling enhance absorption of any topical active ingredient — including copper peptide serums, which have their own evidence base for hair follicle stimulation.
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Consistency over intensity: Six sessions over 12 weeks (biweekly) produced significant results. The takeaway isn't to needle as deeply as possible, but to needle regularly and consistently at an effective depth while allowing proper healing between sessions.
Key Terms Explained
- Dermapen
- An automated microneedling device shaped like a pen, containing a cartridge of fine needles that oscillate vertically at high speed. Unlike a derma roller (which creates angled punctures via rolling motion), a dermapen creates straight, perpendicular channels. The depth can be precisely adjusted, making it ideal for clinical research comparing specific depths. Professional dermapens are typically used in clinical settings.
- Pinpoint Bleeding
- The appearance of tiny blood droplets on the skin surface during microneedling, indicating that the needles have penetrated through the epidermis into the vascular dermis. This is used as a visual endpoint to confirm adequate penetration depth and is considered normal during effective microneedling treatment.
- Biweekly Treatment
- Treatment performed once every two weeks. This frequency allows adequate healing time between microneedling sessions. The skin's wound-healing response takes approximately 7–14 days to complete, so biweekly sessions ensure each treatment benefits from a fully healed baseline while maintaining a therapeutic schedule.
- Randomised Controlled Trial (RCT)
- A study design where participants are randomly assigned to treatment groups, ensuring that the groups are comparable at baseline. This randomisation eliminates selection bias and is considered the gold standard for testing treatment efficacy. In this study, patients were randomly assigned to 0.6mm, 1.2mm, or minoxidil-only groups.
- Hair Diameter
- The thickness of an individual hair shaft, measured in micrometres. Thicker hairs indicate healthier follicle function and contribute more to visible scalp coverage. An increase in hair diameter suggests the treatment is reversing miniaturisation — the progressive thinning of hair shafts that characterises androgenetic alopecia.
- Dermal Papilla
- A cluster of specialised cells at the base of the hair follicle that acts as the follicle's "command centre." It receives blood supply, processes hormonal signals, and directs the hair growth cycle. Growth factors released during microneedling wound healing reach and stimulate the dermal papilla.
- Wnt/β-catenin Pathway
- A biological signalling pathway that plays a critical role in hair follicle development, cycling, and regeneration. Activation of this pathway promotes the transition from resting (telogen) to active growth (anagen) phases and can stimulate the formation of new follicles. Microneedling has been shown to activate this pathway through its wound-healing mechanism.
- Androgenetic Alopecia (AGA)
- The most common form of hair loss, affecting both men and women. It is characterised by progressive miniaturisation of hair follicles driven by genetic sensitivity to dihydrotestosterone (DHT). In men, it typically presents as receding hairline and crown thinning. In women, it usually appears as diffuse thinning across the top of the scalp.
Frequently Asked Questions
Should I use 0.5mm or 0.6mm needles at home?
There is no meaningful clinical difference between 0.5mm and 0.6mm — they are essentially equivalent for practical purposes. Standard at-home derma rollers are typically available in 0.25mm, 0.5mm, 0.75mm, and 1.0mm increments. A 0.5mm derma roller falls squarely within the range that this study found effective. The difference between 0.5mm and 0.6mm is within normal manufacturing tolerance and individual variation in scalp skin thickness. Choose whichever depth is comfortable for consistent use.
If the Dhurat study used 1.5mm and got great results, doesn't that mean deeper is better?
Not necessarily. The Dhurat 2013 study used 1.5mm needles with weekly sessions and achieved dramatic results (+91.4 hairs/cm²). However, that study didn't include a shallower-depth comparator, so we can't know whether the same or better results would have been achieved at 0.5–0.6mm. The Faghihi study specifically made this comparison and found the shallower depth produced better quantitative outcomes. The Xu 2024 meta-analysis subgroup data corroborates this. It's possible that the Dhurat results were driven more by the weekly frequency (vs biweekly here) than by the specific depth.
Can I use a derma roller instead of a dermapen and expect similar results?
This study used an automated dermapen, which creates perpendicular needle insertions. Manual derma rollers create slightly angled punctures due to the rolling motion, which means the effective penetration depth is slightly less than the stated needle length. A 0.75mm or 1.0mm derma roller would likely create channels of similar effective depth to the 0.6mm dermapen setting used in this study. Both devices achieve the same core goals: creating micro-channels for product absorption and triggering the wound-healing growth factor cascade.
How often should I microneedle for hair loss?
This study used biweekly sessions (every 2 weeks) and achieved significant results. The Dhurat study used weekly sessions. Most dermatologists recommend once weekly to once every two weeks for at-home microneedling, depending on the depth used and individual healing speed. Shallower depths (0.5mm) can be used more frequently because they cause less tissue trauma and heal faster. The key is allowing complete healing between sessions — if your scalp is still tender or red from the last session, wait longer before the next one.
Why might deeper needling actually be less effective?
The likely explanation involves the balance between beneficial and harmful inflammation. Microneedling works by triggering a controlled wound-healing response that releases growth factors (PDGF, VEGF, EGF). However, excessive tissue damage from deeper needles can shift the balance toward destructive inflammation — characterised by higher levels of pro-inflammatory cytokines that can actually harm hair follicles and push them into the regression (catagen) phase. The 0.6mm depth may represent the optimal balance: enough penetration to trigger growth factor release while avoiding the excessive inflammation associated with deeper needling.
Does this study apply to female pattern hair loss?
Yes — this study included both men (29) and women (30), making it one of the more gender-balanced microneedling trials for hair loss. While the published results don't separate outcomes by sex, the inclusion of both populations means the overall findings are applicable to both male and female pattern hair loss. The biological mechanisms by which microneedling works — growth factor release, enhanced topical absorption, Wnt pathway activation — are not gender-specific.
Should I still apply my topical serum right after microneedling?
The optimal timing for topical application after microneedling is debated. This study doesn't specify the exact timing of minoxidil application relative to the needling sessions. Some clinicians recommend applying serums immediately after microneedling to take advantage of the open channels, while others suggest waiting 24 hours to allow initial healing. For at-home use with copper peptide serums, applying the serum 4–24 hours after microneedling is a reasonable approach — the channels remain partially open for up to 24 hours, allowing enhanced absorption while minimising the risk of irritation from immediate application on freshly treated skin.
How does needle depth relate to the Xu 2024 meta-analysis findings?
The Xu 2024 meta-analysis performed a subgroup analysis dividing studies by needle depth (above and below 1mm) and found that shallower needles (<1mm) produced a larger effect size (SMD 1.16) than deeper needles (>1mm, SMD 0.52) for hair count outcomes. This independent, pooled analysis across 8 RCTs and 472 patients supports the same conclusion as this Faghihi trial: shallower microneedling is at least as effective — and possibly more effective — than deeper needling. The convergence of a direct comparison trial and a meta-analysis subgroup analysis strengthens this conclusion considerably.
Original Study Citation
Faghihi, G., Nabavinejad, S., Mokhtari, F., Fatemi Naeini, F., & Iraji, F. (2021). Microneedling in androgenetic alopecia; comparing two different depths of microneedles. Journal of Cosmetic Dermatology, 20(4), 1241–1247. https://doi.org/10.1111/jocd.13714
How to Cite This Summary
APA: Hairgenetix. (2025). Microneedling depth: Why shallower needles may work better for hair growth — Plain-language study summary. Hairgenetix Research Library. https://hairgenetix.com/blogs/articles/microneedling-depth-comparison-shallower-better-faghihi-2021
Informal: A 2021 RCT comparing 0.6mm and 1.2mm microneedling depths found that 0.6mm produced greater improvements in hair count (P = 0.017) and thickness (P = 0.007) while causing less pain (Faghihi et al., 2021). Summarised by Hairgenetix at hairgenetix.com.
Last reviewed and updated: March 2025 · Based on original publication: April 2021
The Right Depth, Backed by Research
This study — and the Xu 2024 meta-analysis — confirm what we built the Hairgenetix protocol around: effective microneedling doesn't require painful, deep needling. The evidence shows that shallower depths (0.5–0.6mm) produce equal or superior results with less pain and greater safety.
Our derma roller is designed for this evidence-based approach: creating the micro-channels that enhance copper peptide serum delivery at a depth that's effective, comfortable, and safe for regular home use. Combined with our scientifically formulated copper peptide serum, it's clinical-grade treatment adapted for your routine.
Browse the Hairgenetix Collection →
Microneedling Depth: Why Shallower Needles May Work Better for Hair Growth (2021)
Key Takeaways
Evidence at a Glance
About This Study
Why This Research Matters
By 2021, multiple studies had confirmed that microneedling improves hair growth outcomes when combined with topical treatments. But a critical practical question remained unanswered: how deep should the needles go? Is deeper better — reaching closer to the hair follicle bulb — or is shallower sufficient?
This matters enormously for patients using at-home microneedling devices. Deeper needles (1.0mm+) are more painful, carry higher risk of adverse effects, and are generally recommended only under professional supervision. If shallower depths (0.5–0.6mm) achieve equal or better results, it means effective microneedling is safely achievable at home with standard derma rollers — no clinic visits required.
Faghihi and colleagues designed a head-to-head comparison to answer this question directly. Their finding — that 0.6mm produced better quantitative results than 1.2mm while causing less pain — has significant practical implications for anyone incorporating microneedling into their hair loss regimen.
This finding is also corroborated by the Xu 2024 meta-analysis, which found in its subgroup analysis that needle depths below 1mm produced larger effect sizes (SMD 1.16) than depths above 1mm (SMD 0.52) — strengthening the evidence that shallower is often better.
What The Researchers Did
Faghihi and colleagues recruited 60 patients (29 men and 30 women, aged 18–45) with moderate to severe androgenetic alopecia and randomly assigned them to three groups:
All microneedling sessions were performed every two weeks for 12 weeks (6 sessions total). The treatment endpoint for each session was pinpoint bleeding — the appearance of tiny blood droplets on the scalp surface, indicating the needles have reached the dermis and triggered the wound-healing response.
Results were assessed using four outcome measures:
Understanding the Research Methods
Why a three-group design? By including both a control group (minoxidil only) and two treatment groups (different needle depths), the researchers could answer two questions simultaneously: (1) Does adding microneedling to minoxidil improve results? (2) Does needle depth matter? This is more efficient and informative than running two separate two-group studies.
What is pinpoint bleeding and why is it the endpoint? Pinpoint bleeding — tiny droplets of blood appearing on the scalp surface — indicates that the needles have penetrated through the epidermis into the dermis, where blood vessels and hair follicle structures reside. This confirms adequate penetration depth and triggers the wound-healing cascade that releases growth factors. Using pinpoint bleeding as the session endpoint ensures consistent treatment delivery regardless of individual differences in skin thickness.
Why use an automated dermapen? Unlike manual derma rollers, an automated dermapen (pen-style device) delivers vertical needle insertions at a consistent depth, speed, and angle. This reduces variability between sessions and patients, making the comparison between depths more scientifically valid. The vertical insertion is also less traumatic to tissue than the rolling motion of a derma roller.
Why include both men and women? With 29 men and 30 women, the study evaluated microneedling across both populations — important because most microneedling research has focused on men. Including both sexes increases the generalisability of the findings.
What They Found
Figure 1: Summary of findings from Faghihi et al. (2021). Left: statistical significance of each microneedling depth compared to minoxidil-only controls. Centre: three-group study design showing treatment arms. Right: practical implications of the depth comparison for at-home microneedling. Data source: J Cosmet Dermatol 2021;20(4):1241-1247.
Why Shallower Needles May Work Better: The Biological Explanation
The dermal papilla sweet spot: Hair follicle stem cells and the dermal papilla (the command centre of the follicle) reside in the upper-to-mid dermis, approximately 1–2mm below the scalp surface. However, the growth factor–rich zone — where wound-healing signals trigger follicle stimulation — begins at the junction of the epidermis and dermis, just 0.3–0.6mm deep. A 0.6mm needle reaches this critical zone effectively.
Inflammation balance: Microneedling works through a controlled wound-healing response. Too little penetration doesn't trigger enough growth factor release. But too much penetration can cause excessive inflammation — and chronic or excessive inflammation is actually harmful to hair follicles, potentially pushing them into the catagen (regression) phase. The 0.6mm depth may hit the "sweet spot" of sufficient growth factor stimulation with minimal damaging inflammation.
Micro-channel depth and topical absorption: Microneedling creates temporary channels that allow topical products to penetrate more deeply. Research shows that even relatively shallow channels (0.25–0.5mm) dramatically increase the absorption of topically applied ingredients. The 0.6mm depth creates channels that extend well into the dermis — sufficient for excellent product delivery — without the additional tissue damage of deeper penetration.
Wnt signalling activation: The wound-healing cascade triggered by microneedling activates the Wnt/β-catenin signalling pathway — essential for hair follicle cycling and neogenesis. This pathway activation appears to be triggered effectively at shallower depths, as the relevant stem cell populations are located in the upper follicle region (the bulge area) rather than deep in the dermis.
Clinical Interpretation
This study provides one of the few direct, head-to-head comparisons of microneedling depths for hair loss. Several aspects of the findings deserve careful consideration:
The counterintuitive result makes biological sense: Many people assume "deeper = better" for microneedling. This study challenges that assumption with data showing the opposite trend. The biological explanation — that the relevant targets are in the upper dermis and excessive depth causes counter-productive inflammation — aligns with the findings and with the Xu 2024 meta-analysis subgroup analysis.
Both depths work: It's important to note that both 0.6mm and 1.2mm produced improvements over minoxidil alone. The question isn't whether deeper needles work — they do — but whether the additional depth provides additional benefit. The answer from this trial is no; the additional depth appears to provide no advantage and may actually slightly reduce the treatment effect while increasing pain.
Sample size considerations: With approximately 20 patients per group, this study has moderate statistical power. The fact that significant differences were detected despite the modest sample size suggests the treatment effects are genuinely meaningful. However, the study may have been underpowered to detect a statistically significant difference between the two microneedling depths in a direct comparison.
Corroboration from meta-analyses: The Xu 2024 meta-analysis independently confirmed this pattern: in their subgroup analysis, needle depths below 1mm produced a standardised mean difference of 1.16 versus 0.52 for depths above 1mm. The convergence of evidence from both individual trials and pooled analyses strengthens the conclusion.
How This Compares With Other Research
The Dhurat 2013 landmark study used 1.5mm needles and achieved dramatic results. However, that study used weekly sessions (higher frequency than Faghihi's biweekly) and did not include a shallower-depth comparator. The Xu 2024 meta-analysis subgroup data aligns with Faghihi's finding, suggesting that the dramatic results in the Dhurat study may have been driven more by the weekly frequency than by the specific 1.5mm depth.
Treatment Protocol Details
At-home adaptation: The 0.6mm depth used in this study is within the range achievable with at-home derma rollers (0.25mm to 1.0mm). Most dermatologists recommend 0.5mm to 1.0mm for at-home use, with sessions once weekly to once every two weeks. The key is consistency — maintaining a regular schedule over at least 12 weeks — rather than using aggressive depth or frequency.
Research Limitations to Consider
What This Means For Your Hair
This study directly addresses one of the most common questions people ask about microneedling for hair loss: how deep should the needles be? The answer — supported by this trial and corroborated by the Xu 2024 meta-analysis — is encouraging for anyone using at-home devices:
Key Terms Explained
Frequently Asked Questions
Should I use 0.5mm or 0.6mm needles at home?
There is no meaningful clinical difference between 0.5mm and 0.6mm — they are essentially equivalent for practical purposes. Standard at-home derma rollers are typically available in 0.25mm, 0.5mm, 0.75mm, and 1.0mm increments. A 0.5mm derma roller falls squarely within the range that this study found effective. The difference between 0.5mm and 0.6mm is within normal manufacturing tolerance and individual variation in scalp skin thickness. Choose whichever depth is comfortable for consistent use.
If the Dhurat study used 1.5mm and got great results, doesn't that mean deeper is better?
Not necessarily. The Dhurat 2013 study used 1.5mm needles with weekly sessions and achieved dramatic results (+91.4 hairs/cm²). However, that study didn't include a shallower-depth comparator, so we can't know whether the same or better results would have been achieved at 0.5–0.6mm. The Faghihi study specifically made this comparison and found the shallower depth produced better quantitative outcomes. The Xu 2024 meta-analysis subgroup data corroborates this. It's possible that the Dhurat results were driven more by the weekly frequency (vs biweekly here) than by the specific depth.
Can I use a derma roller instead of a dermapen and expect similar results?
This study used an automated dermapen, which creates perpendicular needle insertions. Manual derma rollers create slightly angled punctures due to the rolling motion, which means the effective penetration depth is slightly less than the stated needle length. A 0.75mm or 1.0mm derma roller would likely create channels of similar effective depth to the 0.6mm dermapen setting used in this study. Both devices achieve the same core goals: creating micro-channels for product absorption and triggering the wound-healing growth factor cascade.
How often should I microneedle for hair loss?
This study used biweekly sessions (every 2 weeks) and achieved significant results. The Dhurat study used weekly sessions. Most dermatologists recommend once weekly to once every two weeks for at-home microneedling, depending on the depth used and individual healing speed. Shallower depths (0.5mm) can be used more frequently because they cause less tissue trauma and heal faster. The key is allowing complete healing between sessions — if your scalp is still tender or red from the last session, wait longer before the next one.
Why might deeper needling actually be less effective?
The likely explanation involves the balance between beneficial and harmful inflammation. Microneedling works by triggering a controlled wound-healing response that releases growth factors (PDGF, VEGF, EGF). However, excessive tissue damage from deeper needles can shift the balance toward destructive inflammation — characterised by higher levels of pro-inflammatory cytokines that can actually harm hair follicles and push them into the regression (catagen) phase. The 0.6mm depth may represent the optimal balance: enough penetration to trigger growth factor release while avoiding the excessive inflammation associated with deeper needling.
Does this study apply to female pattern hair loss?
Yes — this study included both men (29) and women (30), making it one of the more gender-balanced microneedling trials for hair loss. While the published results don't separate outcomes by sex, the inclusion of both populations means the overall findings are applicable to both male and female pattern hair loss. The biological mechanisms by which microneedling works — growth factor release, enhanced topical absorption, Wnt pathway activation — are not gender-specific.
Should I still apply my topical serum right after microneedling?
The optimal timing for topical application after microneedling is debated. This study doesn't specify the exact timing of minoxidil application relative to the needling sessions. Some clinicians recommend applying serums immediately after microneedling to take advantage of the open channels, while others suggest waiting 24 hours to allow initial healing. For at-home use with copper peptide serums, applying the serum 4–24 hours after microneedling is a reasonable approach — the channels remain partially open for up to 24 hours, allowing enhanced absorption while minimising the risk of irritation from immediate application on freshly treated skin.
How does needle depth relate to the Xu 2024 meta-analysis findings?
The Xu 2024 meta-analysis performed a subgroup analysis dividing studies by needle depth (above and below 1mm) and found that shallower needles (<1mm) produced a larger effect size (SMD 1.16) than deeper needles (>1mm, SMD 0.52) for hair count outcomes. This independent, pooled analysis across 8 RCTs and 472 patients supports the same conclusion as this Faghihi trial: shallower microneedling is at least as effective — and possibly more effective — than deeper needling. The convergence of a direct comparison trial and a meta-analysis subgroup analysis strengthens this conclusion considerably.
Original Study Citation
Faghihi, G., Nabavinejad, S., Mokhtari, F., Fatemi Naeini, F., & Iraji, F. (2021). Microneedling in androgenetic alopecia; comparing two different depths of microneedles. Journal of Cosmetic Dermatology, 20(4), 1241–1247. https://doi.org/10.1111/jocd.13714
How to Cite This Summary
APA: Hairgenetix. (2025). Microneedling depth: Why shallower needles may work better for hair growth — Plain-language study summary. Hairgenetix Research Library. https://hairgenetix.com/blogs/articles/microneedling-depth-comparison-shallower-better-faghihi-2021
Informal: A 2021 RCT comparing 0.6mm and 1.2mm microneedling depths found that 0.6mm produced greater improvements in hair count (P = 0.017) and thickness (P = 0.007) while causing less pain (Faghihi et al., 2021). Summarised by Hairgenetix at hairgenetix.com.
Related Research on Hairgenetix
The Right Depth, Backed by Research
This study — and the Xu 2024 meta-analysis — confirm what we built the Hairgenetix protocol around: effective microneedling doesn't require painful, deep needling. The evidence shows that shallower depths (0.5–0.6mm) produce equal or superior results with less pain and greater safety.
Our derma roller is designed for this evidence-based approach: creating the micro-channels that enhance copper peptide serum delivery at a depth that's effective, comfortable, and safe for regular home use. Combined with our scientifically formulated copper peptide serum, it's clinical-grade treatment adapted for your routine.
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