In some cases it may cover as much as half the patient's face. The port wine stain is different from common moles because the skin's pigment cells are not involved in this type of growth. Instead an abnormal cluster of capillaries causes the dark-colored skin. Port wine stains are not cancerous. Causes Common moles are clusters of skin pigment cells that begin growing at the point where the outer layer of the skin meets the layer underneath it.
Freckles have a different origin.
Heredity figures in the tendency to form them, but the freckle itself initially appears in response to sunlight. These moles are unusually large and irregularly shaped, or show other signs that they could become cancerous. But if a mole is growing, becomes irregular in shape, has a mixture of brown, black, or other colors, itches, bleeds, or becomes inflamed or painful, then malignant melanoma may be a possibility. See your doctor as soon as possible if any of these symptoms develop. A doctor should also look at any liver spots that are irregular in shape, uneven in color, or exhibit other unusual symptoms.