Microneedling Infection: Is the Scalp at Risk?

Article Summary

Microneedling is a popular way to combat hair loss and promote hair growth. It creates low levels of inflammation in the scalp tissue, which triggers an adaptive response in the body; growth factors and signaling proteins are recruited for wound repair. However, as with any wound (no matter how small), infections can occur. So what’s the risk of infection from microneedling? And could needle length be a factor? This post aims to answer those questions and provide the best path forward.

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Microneedling for Hair Loss

In the last decade, microneedling has garnered attention in the anti-aging world for its ability to remodel collagen and reduce the appearance of scars. More recently, researchers have started testing microneedling as a treatment for hair loss disorders – including androgenic alopecia.

The process of microneedling creates potentially hundreds of micro wounds on the scalp. This leads to the question: does microneedling for hair loss carry a risk of infection?

How Does Microneedling Work?

In order to assess the risks involved with microneedling, one must understand the process of the procedure. Microneedling – also known as percutaneous wound induction – is the act of deliberately wounding skin tissues for therapeutic benefit. This is generally done with hundreds of tiny, medical-grade needles ranging in lengths from 0.1mm to 5.0mm.

Microneedling evokes low levels of inflammation in the scalp tissue. This inflammation evokes a reaction from the body: growth factors and signaling proteins recruited in wound repair.

Over many wounding sessions (and months), these growth factors and proteins should help to induce new collagen (i.e., skin proteins), create new blood vessels (i.e., angiogenesis), and maybe restore the functionality of damaged skin. As such, repeated microneedling sessions might improve the appearance of scars, wrinkles, and pigmentation disorders.

Does Microneedling Carry a Risk of Infection?

Needle length is especially important when evaluating the risk of infection from microneedling.

The emissary veins in the scalp tissue are the greatest concern when it comes to possible infection. This is because these veins flow bidirectionally through the skull bones and into and out of the brain. These veins reside at least 3 mm beneath the surface of the scalp tissue. If needles puncture these veins, there is a much higher risk of infection.

Staph infections from microneedling have been reported. These cases are likely due to overuse and/or improper sterilization. Dermarollers, pens, and stamps should always be sterilized after every use.

As previously stated, needle lengths used when microneedling can range from less than 0.25mm all the way up to 5mm. However, this is across microneedling practices for all cutaneous conditions and locations, not necessarily hair loss. It’s important to know this context, because the microneedling needle lengths for treating hair loss tend to be much smaller (more on this later).

Moreover, the actual depth of needle penetration depends on a number of factors, such as:

• The microneedling device (i.e., manual roller, stamp, or automated pens)
• User pressure variability (i.e., how hard someone presses down on the device while using it)
• Needle entry angulation (i.e., if the needles penetrate perfectly perpendicular to the skin, or if they enter at another angle)

For these reasons, it’s estimated that microneedling rollers with 1.25-1.5mm needle lengths – when rolled across the scalp – only penetrate 0.6-0.8mm into the skin. For automated pens (which penetrate perpendicular and are less subject to user pressure variability), needle length tends to match needle penetration depth – at least up to 1.5mm.^[1]https://link.springer.com/article/10.1007/s13555-021-00653-2 Nonetheless, these factors matter when accounting for our true risk of penetrating an emissary vein while microneedling and thereby opening ourselves up to a higher risk of infection.

Microneedling for Hair Loss: Which Needle Lengths Have Been Clinically Tested?

Using the longest of these needles would indeed increase the risk of incurring an infection. However, in a 2022 literature review published by our team, we found that investigators testing microneedling for hair loss used needle lengths between 0.5mm-2.5mm.^[2]https://link.springer.com/article/10.1007/s13555-021-00653-2 In that regard, needle penetration depths of 0.6mm to 0.8mm tended to produce the “best” results – at least according to the available data so far.

In that regard, it appears that the optimal needle length for hair-related microneedling is well under 3mm. That’s good news, because it means that our risks for infection are significantly smaller.

In fact, at penetration depths of just 0.6mm to 0.8mm, microneedling barely breaks through the epidermis – which is the outermost layer of skin. In our scalps, it is relatively avascular and constitutes the first 0.4mm to 0.5mm of tissue in our scalps.

At these depths, the risk of infection is incredibly small – particularly if you take simple precautionary measures to properly clean your microneedling device before and after any sessions.

Microneedling for Hair Loss: Best Needle Length

Microneedling for hair loss has promising – albeit limited – data suggesting it is a worthy experimental intervention for certain hair loss sufferers – particularly when paired with minoxidil. The most important factor in considering whether or not there is a risk of infection seems to be the needle length along with how deep those needles will actually penetrate.

The best practices outlined in the literature review include using needle lengths between 0.6mm-0.8mm for automated devices and 1.25mm-1.5mm for manual rollers. When using these needle lengths, the wounds created should fall well short of the emissary veins. Therefore, very little chance of creating a pathway into the bloodstream exists.