Analysis of the Penetration of a Caffeine Containing Shampoo Into the Hair Follicles by In Vivo Laser Scanning Microscopy

The study utilized in vivo laser scanning microscopy to examine the penetration of caffeine from a shampoo into hair follicles. It was found that a 2-minute contact time was sufficient for significant accumulation of caffeine in the follicles, reaching a depth of approximately 200 μm, which is the detection limit of the microscopy used. This depth is where the network of blood capillaries around the follicles begins. Caffeine remained detectable in the follicles even after 24 hours, indicating that hair follicles can serve as a long-term reservoir for topically applied substances like caffeine.