Is sunscreen bad for your skin and did skin cancer not exist until the 20th century?

A former nurse claims that sunscreen bakes chemicals into the skin. She also believes skin cancer only arose in the 20th century due to the American diet.

Two dermatology experts say this is false: Sunscreen either reflects or absorbs the sun's rays, depending on whether it is mineral or chemical sunscreen.

An article in the journal Melanoma Research dates the first key event in melanoma history at around 5 B.C.E., with Hippocrates writing about what is now known as melanoma (according to the article, a word derived from the Greek melas, "dark" and oma "tumor"). 

In 1804, René Laennec, a French physician, first described melanoma as a distinct disease in Paris and coined the term melanose, according to the article.