[paul cotter (OP)]

I don't much look at the gogglebox but others in the house do and I cannot help being exposed to ads for caffeine shampoos. I think this is purely a manufactured "fashion" as I can see no possible benefit for applying an adenosine antagonist to keratin. What do ye think?

[alancalverd]

https://www.theindependentpharmacy.co.uk/hair-loss/guides/what-is-caffeine-shampoo-and-does-it-work-for-hair-loss appears reasonably authoritative even though some of the quoted effects seem contradictory.

A distant male relative not merely avoided baldness but grew particularly luxuriant hair and beautifully soft, smooth skin in his 50's, which he correctly ascribed to  taking some pills that had been prescribed to "cheer up" his wife. All went well until he developed firm, prominent breasts.

I've cut down on caffeine (on the advice of a cardiologist) and adopted a very short razor-cut.   

[paul cotter (OP)]

Thanks for that, Alan. I did notice the contradiction re improved blood flow and vasoconstriction. I thought the article was rather wooly and not definitive but then there may not be a definitive answer. For a polar molecule like caffeine to be significantly absorbed through the skin seems unlikely and I believe much higher levels would be achieved through oral consumption, ie real coffee. Is there any studies linking high coffee consumption with reduced hair loss?

[alancalverd]

It's possible that the surfactant in shampoo aids penetration of caffeine into the follicular sebum, but I'd still prefer to drink it.