Question: is it uva or uvb that tans?
Answer: UVB radiation burns the upper layers of skin (the epidermis), causing sunburns. UVA radiation is what makes people tan. UVA rays penetrate to the lower layers of the epidermis, where they trigger cells called melanocytes (pronounced: mel-an-oh-sites) to produce melanin. Melanin is the brown pigment that causes tanning.