dermatologic disorders
Overview of Effects of Sunlight
Pathophysiology of Sun Exposure
Adverse effects of UV exposure include acute Sunburn and several As a protective response after exposure to sunlight, the epidermis thickens, and melanocytes produce the pigment melanin at an increased rate, causing what is commonly referred to as a "tan." Tanning provides some natural protection against UV radiation but otherwise has no health benefits. People differ greatly in their sensitivity and response to sunlight, based mainly on the amount of melanin in the skin. The skin has been classified into 6 types (I to VI) in order of decreasing susceptibility to sun injury. Classification is based on the interrelated variables of skin color, UV sensitivity, and response to sun exposure (see table). Skin type I is white to very lightly pigmented, very sensitive to UV light, has no immediate pigment darkening, always burns easily, and never tans. Skin type VI is dark brown or black, is most protected from UV light, and is a deep, dark, black-brown color with or without sun exposure. However, dark-skinned people are not immune to the effects of the sun, and darkly pigmented skin can develop sun damage with strong or prolonged exposure. Long-term effects of UV exposure in darker-skinned people are the same as those in lighter-skinned people but are often delayed and less severe because the melanin in their skin provides built-in UV protection. People with blond or red hair are especially susceptible to the acute and chronic effects of UV radiation. Uneven melanocyte activation occurs in many of these fair-haired people and results in freckling. There is no skin pigmentation in people with Albinism because of a defect in melanin metabolism. Patchy areas of depigmentation are present in patients with 