Studies have shown that ~90% of skin cancers can now be directly attributable to ultraviolet light exposure. “It’s not so much that the sun has changed,” explains Dr. Mamelak, “it’s our attitude towards the sun that has changed so dramatically.” The popularity of tanning, for example, is a recent phenomenon, having developed over the last part of the 20th Century. The fashion of having tanned skin did not exist before the 1930s. The persistent popularity of indoor tanning also seems to be a contributing factor. Roughly 400,000 instances of skin cancer per year, including 6,000 melanomas, can be directly attributed to indoor tanning. (Source)