Hair Follicles Contribute Significantly to Penetration Through Human Skin Only Shortly After Application as a Solvent Deposited Solid in Humans
TLDR Hair follicles greatly increase caffeine absorption through the skin shortly after it's applied.
The study aimed to determine the relative penetration of caffeine through hair follicles compared to intact stratum corneum over time in humans. Using pharmacokinetic modeling, it was found that the absorption rate of caffeine through hair follicles was nearly 10 times higher than through the stratum corneum, and hair follicles accounted for more than half of the total absorption. The study also revealed that caffeine absorption through hair follicles occurred within 30 minutes of application and represented 10.5 to 33.8% of the total skin absorption, while absorption through the stratum corneum could take several hours. The conclusion was that hair follicles significantly contribute to the percutaneous absorption of caffeine only shortly after topical application.
