Cells of the skin and underlying tissue may accumulate and cause growths. Growths may be raised or flat and range in color from dark brown or black to flesh-colored to red. They may be present at birth or develop later.
When the growth is controlled and the cells do not spread to other parts of the body, the skin growth (tumor) is noncancerous (benign). When the growth is uncontrolled, the tumor is cancerous (malignant), and the cells invade normal tissue and even spread (metastasize) to other parts of the body. Noncancerous skin growths are often more of a cosmetic problem than anything else.
Doctors do not know what causes most noncancerous skin growths. Some growths, however, are known to be caused by viruses (for example, warts), systemic (bodywide) disease (for example, xanthelasmas or xanthomas caused by excess fats in the blood), and environmental factors (for example, moles or milia stimulated by sunlight).
Last full review/revision September 2008 by Daniel W. Collison, MD