The notion that sun exposure today can promote skin cancer decades from now may suggest to Americans in their 60s and older that additional exposure at their age cannot hurt.

As reasonable as that idea may seem, however, it is misleading, says dermatologist David Sawcer, M.D., Ph.D., assistant professor of medicine at the Keck School of Medicine. Many older Americans increase their outdoor activities after retirement and may not appreciate the potential harm they do to their skin.

"Sun exposure at any age damages the skin," Sawcer says. " Your risk of cancer depends on how much damage you've accumulated from sun exposure and how long you've had it."

"For example, he says, a little bit of damage acquired at a young age and carried for decades can be as much a problem as a lot of damage acquired much later in life.
And although it is hard to say proportionately which is worse, it is clear that both the total length of time a person's skin has been damaged and the severity of the damage play major roles in predisposing a person to skin cancer.

The evidence suggests that developing skin cancer is a multi-stage process in which accumulated sun exposure gradually pushes a person into successive stages.

"If l enter stage one at age 10, I may have 70 more years to accumulate the damage needed to push me into stages two, three and four. But if l enter stage one at age 80, I'd have to be exposed to a lot of sun to race through the successive stages," Sawcer says.