MEDICAL PHYSIOLOGY

Detailed explanation-1: -The outer layer of the skin has cells that contain the pigment melanin. Melanin protects skin from the sun’s ultraviolet rays. These can burn the skin and reduce its elasticity, leading to premature aging. People tan because sunlight causes the skin to produce more melanin and darken.

Detailed explanation-2: -UV radiation induces immediate pigment darkening (IPD) by chemical modification of melanin, and possibly spatial redistribution of melanosomes in keratinocytes and melanocytes (7). UV exposure also leads to delayed tanning (DT) by new synthesis of melanin over several days after UV exposure and persists for weeks (8).

Detailed explanation-3: -Exposure to the UV rays of the sun or a tanning salon causes melanin to be manufactured and built up in keratinocytes, as sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes. The accumulation of melanin in keratinocytes results in the darkening of the skin, or a tan.

Detailed explanation-4: -A direct effect of UV photons on DNA results in up-regulation of the gene for tyrosinase, the rate-limiting enzyme in melanin synthesis, as well as an increase in cell surface expression of receptors for at least one of the several known keratinocyte-derived melanogenic factors, MSH.

Detailed explanation-5: -In most people, UV rays activate a chemical in the skin called melanin. This is the skin’s first defense against the sun. Melanin absorbs the dangerous UV rays that can do serious skin damage. This is the process that gives you a tan.