Definition of Xeroderma pigmentosa:

Xeroderma pigmentosa is a rare condition passed down through families in which the skin and the tissue covering the eye is extremely sensitive to the ultraviolet part of sunlight.

Causes, incidence, and risk factors:

Ultraviolet light -- such as that found in sunlight -- damages the genetic material (DNA) in skin cells. Normally, the body repairs this damage. But in persons with xeroderma pigmentosa, the body does not fix the damage. As a result, the skin gets very thin and patches of varying color (splotchy pigmentation) appear.

The condition also causes spidery blood vessels in the skin (telangiectasia) and skin cancer. Skin cancer often occurs before the child is 5 years old.