Even those who take meticulous care of their skin are likely to develop age- or sun-related imperfections as they grow older. And for many, any new mark or mole kindles skin-cancer concerns. For good reason: Skin cancer is the most common form of cancer in the U.S.

But while skin cancers are increasingly common, a new mole or mark is much likelier to be the benign result of either age- or sun-related damage. Dermatologists say these “age spots” come in four common types. Each of the four has a few defining characteristics, and they all tend to start showing up during a person’s thirties — though they can appear at younger ages.