Caffeine penetrates skin effectively and is typically used at 3% concentration in topical products. It works by breaking down fat cells, protecting against UV damage and aging, improving blood flow to skin, and potentially stimulating hair growth—though the study reviews mechanisms rather than proving real-world effectiveness in humans.

This was a review article examining caffeine's biological activity and how it works in cosmetic formulations, including lab-based skin penetration studies using Franz diffusion cells rather than human trials.

Funding not disclosed in abstract