skin disorders
Hyperpigmentation
Introduction
Hyperpigmentation is darkening of the skin, most often caused by an abnormally high amount of the skin pigment melanin. When exposed to sunlight, specialized skin cells called melanocytes (see Overview of Skin Pigment ) produce increased amounts of the pigment melanin, causing the skin to darken, or tan. In some fair-skinned people, certain melanocytes produce more melanin than others in response to sunlight. This uneven melanin production results in spots of pigmentation known as freckles. A tendency to freckle runs in families. Other factors besides sunlight can cause increased melanin in spots or patches (localized) or in widespread areas of skin. Rarely, other substances besides melanin cause darkening of the skin. 