ABSTRACT
The key role of ultraviolet (UV) radiation in the pathogenesis of the melasma is well established. The depth of penetration of UV light within the skin is wavelength dependent. UVA readily reaches the dermis, including its deeper portions. UVB is absorbed in the epidermis, and only a small proportion reaches the upper dermis. Modern sunscreens were first developed during the 1940s with the primary aim of preventing sunburn. Today, sunscreens are also used to prevent other aspects of photodamage, including carcinogenesis and photo aging. The measure of efficacy of sunscreens is designated the sun protection factor (SPF). Most sunscreens contain a combination of two or more agents created to offer high levels of protection against both UVB and longer-wavelength radiation. Some of the agents are para-aminobenzoic acid and derivatives, cinnamates, salicylates, benzophenones, other organic screens and inorganic screens. The major adverse effects of sunscreens are minor skin irritation, which is common and allergic contact dermatitis, which is rare.
