Interesting research
Caffeine
INCI: Caffeine · also 1,3,7-trimethylxanthine, the coffee molecule
The same molecule in your coffee, applied to the scalp instead of drunk. It is one of the more genuinely strange findings in hair biology, and the strongest data comes from human follicles kept alive in culture.
Why it is here
In cultured human hair follicles, caffeine did something almost rude: it counteracted testosterone-driven growth suppression and stimulated growth on its own. Human follicles, from real scalps, in a lab that could measure it.
Caffeine inhibits phosphodiesterase, which raises intracellular cyclic AMP. In organ-cultured human scalp follicles that translates into longer hair shaft elongation, prolonged anagen and increased matrix keratinocyte proliferation. It also raises IGF-1, which prolongs the growth phase, and lowers TGF-beta 2, which triggers the end of it. Compelling in culture. We are not going to pretend a shower is a laboratory.
The receipts
Testosterone at 5 micrograms per millilitre significantly suppressed follicle growth; caffeine at 0.001 and 0.005 percent counteracted that suppression, and caffeine alone significantly stimulated hair follicle growth, confirmed by Ki-67 staining.
Effect of caffeine and testosterone on the proliferation of human hair follicles in vitro. International Journal of Dermatology, 2007. ex vivo, n = hair follicles from 14 vertex biopsies from male androgenetic alopecia patients. PMID 17214716
Caffeine at 0.0005 to 0.005 percent enhanced hair shaft elongation, prolonged anagen and stimulated matrix keratinocyte proliferation; female follicles were more sensitive than male, and caffeine raised IGF-1 and lowered TGF-beta 2 protein in both.
Differential effects of caffeine on hair shaft elongation, matrix and outer root sheath keratinocyte proliferation, and TGF-beta2 / IGF-1 mediated regulation of the hair cycle in male and female human hair follicles in vitro. British Journal of Dermatology, 2014. ex vivo, n = microdissected male and female human scalp follicles, 120 hours in organ culture. PMID 24836650
What the study actually did
- Study
- Fischer TW, Hipler UC, Elsner P. Effect of caffeine and testosterone on the proliferation of human hair follicles in vitro. 2007.
- Journal
- International Journal of Dermatology 46:27-35
- Design
- Ex vivo organ culture, controlled conditions
- Subjects
- Hair follicles from 14 scalp biopsies, male AGA patients
- Concentration
- 0.001% and 0.005% caffeine
- Duration
- 120 to 192 hours in culture
- Outcome
- Growth suppression by testosterone counteracted; growth stimulated by caffeine alone
In practice
- Typical use
- 0.5 to 2 percent in leave-on scalp products. Note the gap: the culture studies used 0.001 to 0.005 percent in the medium bathing the follicle, which is not the same as a percentage in a rinse-out product on a scalp.
- Pairs with
- Sandalore, Panthenol, Behentrimonium Methosulfate
- Keep apart from
- Nothing chemically. The thing to avoid is the expectation, not an ingredient.
- Cautions
- Topical caffeine at cosmetic levels is not a meaningful systemic dose. None notable otherwise. This is not a hair loss treatment and nothing here should be read as one. If you are losing hair and it bothers you, see a dermatologist.
Questions people ask
Does caffeine regrow hair?
We are not going to say that, because the evidence does not support it. What the evidence shows is that in cultured human scalp follicles, caffeine lengthened hair shaft elongation, prolonged anagen and counteracted testosterone-driven suppression. Those follicles were in an organ culture dish with the caffeine in their medium. That is a laboratory result, not a promise.
Why is caffeine in a conditioner if the evidence is only in vitro?
Because it is genuinely interesting, it is safe, and we would rather tell you exactly what tier it sits in than hide it. Human Condition is a conditioner, not a treatment. Caffeine is in it because the follicle biology is one of the more surprising things in the literature, and because we can cite the dish.
Would drinking coffee do the same thing?
No. The studies applied caffeine directly to the follicle in culture at 0.001 to 0.005 percent in the medium. Oral caffeine distributes through the whole body and reaches the dermal papilla at concentrations nobody has matched to those experiments. Two different routes, two different exposures, and only one of them has been studied this way.