Achieving hair follicle growth under laboratory conditions may not necessary translate to topical application at home. To assess the absorption of caffeine, a study ivestigated the penetration after a 2-min application of 1% caffeine in a shampoo formulation. It was found that caffeine penetrated into the stratum corneum and into the hair follicles. Absorption through the hair follicles and relevant caffeine levels in the blood were already found 5 min after topical application. It was also shown that relatively high levels remained in the blood.
The study artificially blocked some follicles to test determination of the penetration and the absorption of drugs into via the epidermis or the hair follicle. It was found even blocked hair follicles received a transdermally delivered supply of caffeine (fig 1).