Retinol on the scalp and eyebrows: retinoids alongside minoxidil

Dr. Nobakht has said on Instagram that she puts retinol on her eyebrows and scalp, and you've asked a lot about it. This article explains why — and what isn't settled yet.

How does minoxidil get activated?

To work, minoxidil has to be converted inside the hair follicle into its active form, minoxidil sulfate. An enzyme called SULT1A1 does this. People whose follicles have low activity of this enzyme usually respond less well to minoxidil.

Tretinoin and the SULT1A1 enzyme

Studies on tretinoin (a prescription retinoid) have shown it can increase this enzyme's activity. In a small 2019 study, five days of topical 0.1% tretinoin moved 43% of people who were predicted not to respond to minoxidil into the responder group. So some people with a weak response to minoxidil may respond better when tretinoin is added. The study was small, and more research is needed.

What about retinol?

In the skin, retinol is eventually converted to retinoic acid (tretinoin). In laboratory studies on human hair follicles, retinol plus minoxidil promoted follicle growth more than minoxidil alone. These are lab results, and clinical studies are still needed.

There's no standard dose of retinol for the scalp yet. Dr. Nobakht herself uses 0.1% retinol every other night and adjusts to how her skin tolerates it.

Points of caution

• Retinoids can cause redness, flaking or stinging; if your skin gets irritated, use them less often.
• Tretinoin is a prescription medicine, and its timing and combination with minoxidil should be set with your doctor.
• Retinoids make skin more sensitive to the sun; don't forget sunscreen on your face and eyebrows.

References

• Sharma A, et al. Tretinoin enhances minoxidil response in androgenetic alopecia patients by upregulating follicular sulfotransferase enzymes. Dermatologic Therapy, 2019 — doi.org/10.1111/dth.12915
• Kwon OS, et al. The additive effects of minoxidil and retinol on human hair growth in vitro. Biological & Pharmaceutical Bulletin, 2007 — pubmed.ncbi.nlm.nih.gov/17202653
• Kwon OS, et al. Promotive effect of minoxidil combined with all-trans retinoic acid (tretinoin) on human hair growth in vitro. Journal of Korean Medical Science, 2007 — pmc.ncbi.nlm.nih.gov/articles/PMC2693596