Does caffeine shampoo actually work for hair loss? What the evidence says

What did the caffeine studies actually do?

Both were organ culture: human scalp hair follicles kept alive in a dish and bathed in medium. In 2007, Fischer, Hipler and Elsner took follicles from 14 vertex biopsies from men with androgenetic alopecia. Testosterone at 5 micrograms per milliliter significantly suppressed follicle growth. Caffeine at 0.001% and 0.005% counteracted that suppression, and caffeine alone significantly stimulated follicle growth, confirmed by Ki-67 staining for proliferating cells.

The 2014 paper in the British Journal of Dermatology, again led by Fischer, is the stronger of the two. Microdissected male and female scalp follicles were cultured for 120 hours with testosterone, with and without caffeine at 0.0005% to 0.005%. Caffeine enhanced hair shaft elongation, prolonged the growth phase, stimulated matrix keratinocyte proliferation, raised IGF-1 protein, which prolongs growth, and lowered TGF-beta 2, which triggers the end of it. Female follicles were more sensitive than male.

How would caffeine work on hair?

Caffeine inhibits phosphodiesterase, which raises cyclic AMP inside cells. In the follicle that translated into the changes above: longer elongation, a longer anagen phase, more proliferation in the matrix, more IGF-1 and less TGF-beta 2. It is a coherent mechanism and it is one of the more genuinely strange findings in hair biology. It is also, so far, a finding about follicles in a dish.

What is the gap between a dish and a shower?

Concentration and time. The culture studies used 0.0005% to 0.005% caffeine in the medium bathing the follicle continuously for 120 to 192 hours. A leave-on scalp product typically carries 0.5% to 2%, and a rinse-out conditioner is in contact with the scalp for a minute or two before it goes down the drain. Those are not the same exposure, and a percentage on a label is not the same as a concentration at the follicle. Our ledger contains no human trial of caffeine in a rinse-out product, so we do not pretend to one.

• Studied: continuous exposure of cultured follicles for 5 to 8 days.
• Sold: a minute of contact in a shower.
• Missing: a human trial of caffeine in a rinse-out product.

So does caffeine shampoo work for hair loss?

We do not know, and neither does anyone selling it. The laboratory evidence is real and interesting. The human evidence for washing it on and rinsing it off does not exist in our ledger. Caffeine 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, because the treatments with human trials behind them are prescription and a conditioner is not going to replace them.

What we made with it

Human Condition, which comes after the five face products, is a cleansing conditioner built for the scalp first, because the scalp is skin and it gets washed harder than any other skin you own. The conditioning is done by behentrimonium methosulfate and cetearyl alcohol, the body by panthenol and hydrolyzed protein. Caffeine is in it because the research is strange enough to be interesting, the ingredient is gentle, and we would rather tell you exactly what kind of research it is than let a percentage on the label do the implying.

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