Tanning, either by the sun or by artificial means, is hugely popular in the United States and elsewhere. The word itself is interesting, deriving from the Old English tannian which in turn is derived from the Latin tannum, meaning oak bark. This makes sense, because the inner bark of certain oaks are rich in phenolic compounds that have been and still are used to tan raw skins into leather.
During the tanning process the skins darken, just like the human skin usually darkens when exposed to the ultraviolet light in sunlight or tanning salons. I use the term usually because some very fair people never tan but just burn, and very dark skinned people show little or no tanning. Albinos are not capable of tanning.
Before we get to the science behind tanning, it is of service to look at the cultural aspects of it. There has been a sea change in attitudes about tanning in the past century. I shall use my mum as an example.