Ultraviolet B (UVB) rays can cause serious damage to the DNA or genetic material of skin cells, making up approximately 5 percent of the sun's rays that reach the skin. Every year, more new cases of skin cancer are diagnosed in the U. S. than the new cases of breast, prostate, lung and colon cancer combined.
It is estimated that one in five Americans will develop skin cancer at some point in their lives, with an American dying from skin cancer every hour. Unprotected exposure to UV radiation is the most preventable risk factor for skin cancer. Epidermal melanization blocks the penetration of UV rays into the skin, reducing cumulative doses of UV rays and reducing mutagenesis and the risk of cancer. People who may be exposed to artificial sources of UV rays at work should follow appropriate safety precautions, including wearing protective clothing and UV protectors and filters.
New knowledge about the ways in which the MC1R and other genes work to protect the skin against the harmful consequences of UV rays could allow for the rational development of pharmacological strategies to reduce UV sensitivity and the risk of cancer. People with MC1R gene defects receive higher doses of UV radiation because their skin is less able to block UV photons, and they can also accumulate more mutations due to faulty DNA repair caused by UV exposure. However, UV rays are also beneficial to human health by mediating the natural synthesis of vitamin D and endorphins in the skin, so UV rays have complex and mixed effects on human health. As a component of the electromagnetic spectrum, UV photons fall between the wavelengths of visible light and gamma radiation.
The dose of ambient ultraviolet radiation varies according to the amount of atmosphere it passes through, making UV radiation doses higher near the equator (where sunlight hits the Earth most directly), at higher altitudes, and under conditions of minimal cloud or particle coverage. People with fair skin with low levels of melanin in the epidermis show a UV-sensitive phenotype, which tends to burn rather than tan after exposure to UV rays. Sunlight is the main source of UV radiation, although it only makes up a small part of its rays. People with light skin pigmentation suffer comparatively more skin damage from UV rays, as it is relatively easy for them to penetrate the epidermis and damage both keratinocytes and melanocytes in deeper layers.
