The sun emits ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC) rays. However, UVC rays do not have any effect on the skin because they are completely absorbed by atmospheric ozone and, hence, do not reach the skin. UVA and UVB rays on the other hand do reach the earth and can penetrate your skin quite quickly, to harmful effect. Medline Plus says that ultraviolet rays from the sun can affect your skin during any season and at any temperature.
Skin Cancer
According to the Mayo Clinic, skin cancer is the abnormal growth of skin cells that often develops on sun-exposed skin. The top layer of the skin (the epidermis) is made of three types of cells: squamous, basal and melanocytes. The cells of the epidermis are constantly being shed and replaced by new cells. This process is controlled by the DNA of the skin cells. However, UVB radiation from the sun, tanning beds or lamps is capable of causing skin cancer because it kills skin cells and damages the DNA of skin cells while UVA radiation weakens the immune system of the skin.
Damaged DNA may lead to overgrowth of new skin cells while skin cells killed off by UVB rays lead to sunburn---a risk factor for skin cancer. These processes increase the risk of developing skin cancer. Squamous cell and basal cell carcinoma along with melanoma are the most common types of skin cancer.
Early Aging and Skin Appearance
UV radiation affects the appearance of the skin because it induces signs of early aging, such as wrinkled skin, leathery skin and age spots. When UVA light penetrates your skin, it damages the collagen and elastin, which give the skin strength, firmness and elasticity. Damage to proteins in the skin lead to early aging.
UVB rays stimulate production of skin cells, which results in thick leathery skin. Both types of UV rays induce production of melanin---the pigment that gives skin its color; however, excessive production of melanin in one spot on the skin or too many melanin producing cells in one area of the skin cause age spots---flat, brown, black or gray spots on the skin.
Allergic Reactions
Some individuals are sensitive to the rays of the sun. For these people, sun exposure may cause allergic reactions in the form of rashes, hives, blisters or red blotches on the skin. Certain medications may cause allergic reactions when the skin is exposed to UV radiation. Some of these sun-sensitive medications include oral anti-diabetics, birth control pills, tranquillizers, painkillers, antidepressants and antibiotics, as stated by the World Health Organization.
