UV radiation from the sun is a major environmental factor that affects skin pigmentation. When the skin is exposed to UV radiation, the body produces more melanin in an effort to protect the skin from damage. This process is called melanogenesis, and it leads to a temporary darkening of the skin, which is commonly referred to as a "tan." The increased production of melanin occurs as a result of a complex biological process that involves a series of chemical reactions within the melanocytes. UV radiation stimulates the production of a hormone called alpha-melanocyte-stimulating hormone (α-MSH), which binds to receptors on the surface of the melanocytes and triggers the production of melanin. The type and amount of melanin produced in response to UV radiation can vary depending on a person's genetics, skin type, and the intensity and duration of sun exposure. People with fair skin are more susceptible to sunburn and skin damage from UV radiation, and may develop a sunburn rather than a tan if they are not adequately protected. Excessive exposure to UV radiation over time can lead to long-term changes in skin pigmentation, including hyperpigmentation (darkening of the skin) and the development of age spots or sunspots. UV radiation can also damage the DNA in skin cells, leading to mutations that can increase the risk of skin cancer. To minimize the effects of UV radiation on skin pigmentation, it is important to protect the skin from the sun by wearing protective clothing, using sunscreen, and avoiding prolonged exposure to the sun, particularly during peak UV hours (10 a.m. to 4 p.m.). It is also important to be aware of any changes in skin pigmentation, and to seek medical advice if you notice any unusual or persistent changes in the appearance of your skin.