Am I Supposed to Bleed When Microneedling? A Scientific Analysis

Whether microneedling is done by a dermatologist or at home, how deep do the punctures need to be for the best results? Is bleeding when microneedling necessary, or is it a sign that it’s being done incorrectly? This guide explores how needle depth affects the efficacy of microneedling and whether bleeding needs to be involved in achieving the best results.

What is Microneedling?

Microneedling, a minimally invasive cosmetic procedure, has gained recognition for its potential to enhance outcomes in individuals with androgenic alopecia (AGA). This approach involves specialized devices equipped with fine, tiny needles that create controlled micro-injuries on the scalp’s surface. While intentionally inducing micro-injuries may seem counterintuitive, it triggers the body’s natural wound-healing response, fostering numerous processes that benefit individuals with AGA.

Microneedling can be conducted either in a clinical setting or at home. Various devices are available for this purpose, including needling stamps, manual rollers, and automated pens. Some of these devices may incorporate fractional radiofrequency technology. Regardless of the specific device used and the needling depth, microneedling has proven effective in clinical settings as both a primary treatment and a complementary therapy.

What Evidence Supports the Use of Microneedling?

Clinical studies have demonstrated that microneedling can increase hair density, thickness, and count in individuals with AGA. A landmark study was conducted by Rachita Dhurat in 2013 on 100 subjects with AGA, using a 1.5 mm derma roller. The researchers found that over 12 weeks, once weekly microneedling combined with twice daily 5% minoxidil significantly increased hair counts compared to minoxidil treatment alone (Figure 1).^[1]Dhurat, R., Sukesh, M.S., Avhad, G., Dandale, A., Pal, A., Pund, P. (2013). A Randomized Evaluator Blinded Study of Effect of Microneedling in Androgenetic Alopecia: A Pilot Study. International … Continue reading

Figure 1: Microneedling plus 5% minoxidil for AGA: results over three months (weekly sessions).^[2]Dhurat R., Sukesh, M.S., Avhad, G., Dandale, A., Pal, A., Pund, P. (2013). A Randomized Evaluator Blinded Study of Effect of Microneedling in Androgenetic Alopecia: A Pilot Study. International … Continue reading

Further research has continued to investigate the mechanism of action of microneedling on hair growth, as well as its effects on hair regrowth.

We have covered many of these studies (and more) in our systematic review on the subject (which was published in Dermatology and Therapy in 2021).^[3]English Jr, R.S., Ruiz, S., DoAmarel, P. (2022). Microneedling and its use in hair loss disorders: A systematic review. Dermatology and Therapy. 12. 41-60. Available at: … Continue reading

Microneedling is generally done with hundreds of tiny, medical-grade needles ranging from 0.1mm to 5.0mm, determining how far into the skin the needles penetrate.

A derma roller for at-home microneedling.

The skin comprises three main layers: the epidermis, dermis, and hypodermis (Figure 3).

Figure 3: The layers of the skin.^[6]Yousef, H., Alhajj, M., Sharma, S. (2022). Anatomy, Skin (Integument), Epidermis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; Available from: … Continue reading

Epidermis

The epidermis is the outermost layer of skin, and its thickness can vary from 0.04-0.4 mm in different body areas to serve various functions.^[7]Skandalakis, L.J. (2009). Skin, Scalp, and Nail. In: Surgical Anatomy and Technique. Springer, New York, NY. Available at: https://doi.org/10.1007/978-0-387-09515-8_1 On the scalp, the epidermis plays a role in protecting the underlying tissues and structures, including the hair follicles; however, it is usually avascular (meaning that it doesn’t have any blood vessels running through it). The epidermis gets its nutrients and disposes of waste products via diffusion from/to the underlying dermis.^[8]Kim, J.Y., Dao, H. (2023). Physiology, Integument. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available at: https://www.ncbi.nlm.nih.gov/books/NBK554386/ (Accessed: 6 … Continue reading

Dermis

The dermis is the layer of skin located just beneath the epidermis on the scalp. It plays a crucial role in supporting hair growth and overall scalp health.

The primary functions of the scalp dermis include:

• housing hair follicles
• providing nourishment to the hair bulb through blood vessels
• anchoring hair follicles to the underlying structures

The scalp dermis is also responsible for regulating temperature and protecting the hair follicles. In terms of thickness, the dermis is the thickest and can range from  1.5 – 4 mm deep.^[9]National Cancer Institute (no date). Layers of the Skin. National Cancer Institute. Available at: https://training.seer.cancer.gov/melanoma/anatomy/layers.html (Accessed: 6 November 2023)

Hypodermis

The scalp hypodermis, or subcutaneous layer, is the deepest layer of the scalp skin. Its role is primarily related to insulation, energy storage, and providing cushioning and protection for the underlying structures, such as the skull and blood vessels. The hypodermis is rich in fat cells, blood vessels, and connective tissue. This layer helps regulate temperature, acts as an insulator, and stores fat as an energy reserve. The thickness of the scalp hypodermis can vary from person to person, but it’s typically a few millimeters deep. Maintaining a healthy scalp hypodermis is crucial for overall scalp function and protection.

Do I Need to Bleed for Microneedling To Work?

The short answer is no; bleeding is not a requirement for effective microneedling. However, pinpoint bleeding from microneedling is not necessarily detrimental, and it can just be wiped away.

Excessive bleeding, however, can be an indication that the needles are penetrating too deeply, which may increase the risk of side effects and is not necessary for the therapeutic benefits of the procedure. Emissary veins are vessels that connect the hypodermis of the scalp to the brain through the skull, functioning in both directions.^[10]Klein, B.M., Bordoni, B. (2023). Anatomy, Head and Neck, Emissary Veins. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available at: … Continue reading Infections in the brain stemming from scalp injuries often result from these veins being compromised, allowing bacteria from the skin to enter the brain, potentially leading to severe consequences or even death.

These veins are not uniformly distributed across the scalp and are typically found deeper than 5 mm, near the lower regions of the hypodermis. There’s no need to risk damaging these veins with microneedling since activating the hair follicle’s stem cell bulge is possible at shallower depths, specifically between 1.5 mm and 2.5 mm.

The existing research on microneedling for hair loss does not involve needles longer than 2.5 mm, so it is advisable to stick within these clinically supported depths and avoid going deeper.

Microneedling: What Depth Of Punctures Will Cause Bleeding?

As mentioned above, our skin is segmented by three primary layers: the epidermis, dermis, and hypodermis. The epidermis is the outermost layer of skin and is relatively avascular (without microcapillary networks). The epidermis of scalp skin is estimated to be 0.4mm deep. So, most wounds at this depth and shallower do not bleed. However, you may not get the full beneficial effect from microneedling at this depth. It is only after this depth that punctures from microneedling might evoke erythema, swelling, or pinpoint bleeding.

What’s the Best Needle Depth?

While penetrating the epidermis may be beneficial for increasing drug penetration, it is avascular. Therefore, to produce an appreciable inflammatory response in scalp skin, penetration past the epidermis is necessary. But how far should we go? Well, not much further, according to one study.

Which Needle Length Is Better: 0.6 mm or 1.2 mm?

One study compared two depths of microneedling, 0.6 mm and 1.2 mm, in 60 participants aged 18-45 with mild-to-moderate alopecia. The participants were divided into three groups. One group was treated with only 5% minoxidil lotion, the second group (group A) received minoxidil plus biweekly microneedling at a depth of 1.2 mm and the third group (group B) received minoxidil plus biweekly microneedling at a depth of 0.6 mm over 12 weeks.^[11]Faghihi, G., Nabavinejad, S., Mokhtari, F., Naeini, F.F., Iraji, F. (2020). Microneedling in androgenetic alopecia; comparing two different depths of microneedles. Journal of Cosmetic Dermatology. … Continue reading

Results

Both hair count and thickness significantly increased in all groups compared to the baseline, with group B showing a substantially more significant increase in hair count and thickness than the control group (Figure 4). Additionally, hair regrowth evaluated by investigators was significantly higher in both microneedling groups compared to the minoxidil group, with group B (0.6 mm depth) tending to show more benefit than group A (1.2 mm depth). This improvement was not statistically significant, however, and the 1.2 needle improved hair counts by about 15%, and the 0.6 mm needle improved hair counts by about 19%.

Figure 4: The effect of needle depth on mean hair count (white bar) and thickness (black bar).^[12]Faghihi, G., Nabavinejad, S., Mokhtari, F., Naeini, F.F., Iraji, F. (2020). Microneedling in androgenetic alopecia; comparing two different depths of microneedles. Journal of Cosmetic Dermatology. … Continue reading

So, we can see that the 0.6 mm needle length was superior at improving hair counts and thickness, but what other benefits might we see from using the shorter needle length?

Other Benefits

Reduced Pain: According to the study,  participants in group A (1.2 mm depth) reported more severe pain than the other groups. Therefore, using a shorter needle may reduce the pain associated with microneedling.

Less Trauma to Hair Follicles: It was speculated in the study that the deeper penetration of needles from group A might have caused some trauma to the hair bulge, thus decreasing its efficacy, indicating that shorter needle length may be more beneficial for overall hair follicle health.

Faster Wound Healing: Because the 0.6 mm needle depth does not penetrate as far, it is likely that wound healing will be faster (although this wasn’t examined in this study).

Other Studies

Interestingly, other studies have suggested that using a derma roller with 1.5 mm-sized needles also might improve hair growth for those with androgenic alopecia.^[13]Jha, A.K., Udayan, U.K., Roy, P.K., Amar, A.K.J., Chaudhary, R.K.P. (2018). Original article: Platelet-rich plasma with microneedling in androgenetic alopecia along with dermoscopic pre-and … Continue reading,^[14]Dhurat, R., Sukesh, M.S., Avhad, G., Dandale, A., Pal, A., Pund, P. (2013). A Randomized Evaluator Blinded Study of Effect of Microneedling in Androgenetic Alopecia: A Pilot Study. International … Continue reading

Furthermore, needle penetration studies show that with microneedling automated pens, needling depths matched penetration depths up to 1.5 mm (meaning that the needle will penetrate to the exact depth).^[15]Sasaki GH. (2017). Micro-needling depth penetration, presence of pigment particles, and fluorescein stained platelets: clinical usage for aesthetic concerns. Aesthetic Surgery Journal. 37(1):71–83. … Continue reading

However, when it comes to manual rollers, it’s estimated that due to pressure variability and angle of needle entry, microneedling rollers may only penetrate to skin depths of 50-70% of its needle length.^[16]de Andrade Lima, E.V., de Andrade Lima, M. (2013). Microneedling experimental study and classification of the resulting injury. Surgical and Cosmetic Dermatology. 5(2). 110-114.

Therefore, to achieve an optimal depth of around 0.6 – 0.8 mm (based on the available clinical data), an automated pen set to 0.6 -0.8 mm or a manual roller set to 1.00 – 1.5 mm (to account for the loss of penetration) may be the most beneficial.^[17]English Jr, R.S., Ruiz, S., DoAmarel, P. (2022). Microneedling and its use in hair loss disorders: A systematic review. Dermatology and Therapy. 12. 41-60. Available at: … Continue reading

Does Bleeding From Microneedling Improve Hair Growth Outcomes?

When looking at the methodologies across microneedling studies, we can see that investigation groups used various methods to denote the endpoint of any microneedling session.^[18]English Jr, R.S., Ruiz, S., DoAmarel, P. (2022). Microneedling and its use in hair loss disorders: A systematic review. Dermatology and Therapy. 12. 41-60. Available at: … Continue reading Aside from using different microneedling devices and needle lengths, research groups also tended to vary their session endpoints based on:

• A set number of roller passes in any given area.
• Any number of passes horizontally, vertically, and diagonally until mild erythema (pink skin) occurred
• A set time limit (from just a few minutes to 45 minutes)
• The arrival of pinpoint bleeding

Despite the various methodologies across studies, microneedling led to similar ballpark hair parameter improvements. For these reasons, it’s unclear if pushing harder when microneedling or generating more acute inflammation via pinpoint bleeding induces better outcomes. 

Based on the data available, there is nothing to suggest that bleeding when microneedling is necessary and worth the additional pain.

What If I’m Combining Microneedling With Topicals?

Microneedling’s mechanisms of action may change depending on the needle penetration depth.

• At shallower depths (0.5mm and lower), microneedling punctures the scalp’s epidermis. This can significantly enhance the efficacy of minoxidil by increasing both (1) dermal absorption of the drug and (2) sulfotransferase activity. Sulfotransferase is the enzyme required to activate minoxidil.
• At deeper depths (0.5mm-2.0mm), microneedling punctures into the dermis and evokes a stronger acute inflammatory reaction. This can induce growth factors, signaling proteins, and hormones linked to the anagen (growth) stage of the hair cycle.

If using microneedling alongside minoxidil, it’s possible to still benefit from microneedling with shorter needle lengths. Shorter needle lengths still produce the benefits of microneedling via enhancement of topical absorption and activation. Shallow microneedling will also minimize the pain associated with a microneedling session and help avoid bleeding. 

So, no, it is not a requirement to bleed when microneedling to get the best results. But if bleeding occurs? Just wipe the blood away with an alcohol swab.