Caffeine at 3% concentration can penetrate skin effectively and works by breaking down fat cells, boosting blood flow, and protecting against UV damage and aging. It also has antioxidant properties and may stimulate hair growth by blocking an enzyme involved in hair loss.

This was a review study examining existing research on how caffeine works in topical products, including lab experiments using Franz diffusion cells to test how well it penetrates skin.

Funding not disclosed in abstract