Hyperpigmentation is the increase in the natural color of the skin. Melanin, a brown pigment manufactured by certain cells in the skin called melanocytes, is responsible for skin color. Melanin production is stimulated by a pituitary hormone called melanocyte stimulating hormone (MSH). Other pigments appear in the skin much less often. Melanin gives skin its natural color.

Darkened spots on the skin come in several varieties. The most ominous is malignant melanoma, a very aggressive cancer that begins as an innocent mole. Most moles (nevus), however, are and remain benign (harmless). The average person has several dozen, and certain people with a hereditary excess may have hundreds. Freckles, age spots, and cafe au lait spots, known as ephelides, are always flat and not as dark. Cafe au lait spots are seen mostly in people with another hereditary disorder called neurofibromatosis. "Port wine stains" are congenital dark red blotches...