Ketotifen decreases the release of bioactive mediators, such as leukotrienes, histamine, and proteases. It has been suggested as a treatment for photoaging after being found to prevent mast cell deposition, degranulation, skin thickening, and wrinkles in UV irradiated hairless mice. Famotidine is an H2-receptor antagonist that suppresses histamine-mediated melanogenesis and dendricity in cultured human melanocytes, whereas H1 and H3 antagonists have no inhibitory effect.