How Does Latanoprost Work to Make Eyelashes and Possibly Scalp Hair Grow?

When we talk about latanoprost, we are talking about a drug that was never intended to make eyelashes grow. The FDA approved it in 1996 strictly as an eye drop for glaucoma, a condition that increases pressure inside the eye and can damage the optic nerve. The drug’s real job is to mimic prostaglandins, natural molecules in our body that regulate inflammation, circulation, and, as it later turned out, even hair follicle behavior. The curiosity began when patients treated for glaucoma started to notice that their eyelashes looked longer, darker, and denser. What began as an unintended effect in ophthalmology quietly entered the field of cosmetic science.

The Biological Mechanism Behind the Growth

To understand why eyelashes change under latanoprost, we need to talk about the hair growth cycle. Hair does not grow continuously. It passes through phases: anagen (growth), catagen (transition), and telogen (resting). The balance of these phases determines whether hair actively lengthens or simply sheds and falls out. Prostaglandins influence this cycle by pushing follicles into the anagen phase and keeping them there longer than usual. Latanoprost, as a prostaglandin analog, appears to extend this growth phase. In practice, this is why eyelashes exposed to the drug become longer and thicker. The same principle could, at least in theory, apply to scalp hair, but the evidence here is less convincing.

Reports of eyelash growth are not anecdotal; they have been observed systematically. In 2002, Johnstone and Albert described prostaglandin-induced hair growth in Survey of Ophthalmology. Their work was based on patient observations, not controlled experiments, but it confirmed a consistent link between prostaglandin analogs and eyelash changes. In 2009, Yamamoto and colleagues studied 54 glaucoma patients treated with latanoprost over a period of twelve months. Using slit-lamp photography, they documented measurable increases in eyelash length and pigmentation. However, the population was relatively small and limited to patients already under treatment for an eye condition. The results were convincing for eyelashes, but they do not automatically translate to other types of hair.

What Happens When We Test It on Scalp Hair?

The scalp is different from the eyelid. While eyelashes grow in short cycles of a few months, scalp hairs can remain in the anagen phase for years.

This makes the biology more complex. A pilot study conducted by Blume-Peytavi et al. in 2012 investigated the topical application of latanoprost 0.1% on the scalp of 16 men with mild androgenetic alopecia. For 24 weeks, the drug was applied to small patches of the scalp, and results were evaluated with macrophotography and hair counts. The outcome was a modest but statistically significant increase in hair density compared to placebo. Yet the limitations were impossible to ignore: the study was small, lasted less than six months, and covered only localized scalp areas. We cannot take these findings as evidence of a reliable treatment.

Animal studies reinforce this mixed picture. Uno and colleagues in 2002 tested topical latanoprost on macaque monkeys with bald patches. Over several months, they observed increased hair density and thickness. While this supports the biological plausibility, monkeys and humans do not share identical hair growth cycles. Translation to human scalp remains speculative.

Why Isn’t It Used Widely for Baldness?

If latanoprost can make eyelashes grow, why isn’t it already a treatment for hair loss? The answer lies in evidence and practicality. For eyelashes, we have consistent clinical reports and visible results within months. For scalp hair, the evidence remains limited to small pilot studies and animal models. The FDA has not approved latanoprost for hair loss, which means its use outside the eye remains off-label. Applying eye drops to a small eyelid margin is practical. Spreading a similar solution across an entire scalp daily is not. On top of that, treatments like minoxidil and finasteride already dominate the field of hair loss, with decades of large-scale trials supporting them. Latanoprost has not reached that level of validation.

What we need to know is simple: latanoprost works reliably for eyelashes because it directly affects short-cycle hairs with a quick turnover. When applied to the scalp, it shows potential but in weak, inconsistent, and under-researched ways. Technical terms like “prostaglandin analog” or “hair growth cycle” describe real mechanisms, but translating them into a guaranteed treatment is not yet justified. The science is still too narrow in scope, with limited populations, short timelines, and methodological gaps. Until larger and longer studies are conducted, latanoprost for scalp hair growth remains an interesting but unproven possibility.

References

Blume-Peytavi, U., Lönnfors, S., Hillmann, K., Garcia Bartels, N., & Vahlquist, A. (2012). A randomized, double-blind, vehicle-controlled, pilot study to assess the efficacy and safety of latanoprost 0.1% on hair growth in healthy males with androgenetic alopecia. British Journal of Dermatology, 166(2), 436–438. Retrieved from https://pubmed.ncbi.nlm.nih.gov/21910708/

Johnstone, M. A., & Albert, D. M. (2002). Prostaglandin-induced hair growth. Survey of Ophthalmology, 47(Suppl 1), S185–S202. Retrieved from https://pubmed.ncbi.nlm.nih.gov/12204717/

Uno, H., Kurata, S., & Ueda, S. (2002). Effects of topical latanoprost on hair growth in the bald scalp of the macaque monkey. Journal of the American Academy of Dermatology, 46(4), 596–602. Retrieved from https://pubmed.ncbi.nlm.nih.gov/11907444/

Yamamoto, T., Itonaga, K., & Osada, A. (2009). Eyelash changes in patients treated with latanoprost. Japanese Journal of Ophthalmology, 53(1), 15–19. Retrieved from https://pubmed.ncbi.nlm.nih.gov/19189118/