Caffeine

Caffeine has antioxidant properties that reduce free radical formation and may help prevent UV-induced skin damage. It is associated with improving microcirculation, which is theorized to help with dark under-eye circles and puffiness, though double-blind research on a 3% caffeine gel found no significant difference from its gel base alone. It is also used for potential anti-cellulite effects via lipolysis stimulation and for hair growth, with one 2017 study finding a 0.2% caffeine liquid non-inferior to 5% Minoxidil in men with androgenetic alopecia.

Some claimed benefits (puffy eyes, anti-cellulite) are more hyped than backed by robust human clinical data; evidence for anti-cellulite effects is largely limited to animal studies or combinations with other actives.