Every day the sun emits ultraviolet (UV) radiation of three different types: short-wave UV-C, medium-wave UV-B and long-wave UV-A . The ozone that surrounds the earth absorbs all of the UV-C radiation, and a large portion of the UV-B radiation. The remaining UV-B and all UV-A radiation affect human skin cells on a daily basis. This UV radiation leads to a variety of damaging effects in human cells.
Skin Cancer
Skin cancer refers to uncontrolled cell growth of damaged cells in skin tissue. The University of Maryland Medicine recognizes three main types of skin cancer--basal cell carcinoma, squamous cell carcinoma and malignant melanoma. The mechanism for developing skin cancer lies in genetic mutation in a type of skin cell called keratinocytes. According to a study done at the M.D. Anderson Cancer Center by Allal Ouhtit and Honnavara N. Ananthaswamy, prolonged UV radiation damage causes pyrimidine bases, cytosine and thymine, to change places in the deoxyribonucleic acid (DNA) sequence; a thymine becomes a cytosine or a cytosine becomes a thymine in cell cycle genes. These mutations cause programmed cell death--a normal cell process which reduces the amount of mutated DNA being replicated--to halt. Mutated cells that do not die off can replicate uncontrollably. These nucleic acid base changes result from radiation in the UV-B spectrum.
Human skin cells possess mechanisms capable of repairing a large amount of DNA damage. Problems occur when the UV radiation mutates the genes responsible for DNA repair. Mutated DNA repair machinery genes do not get transcribed into the protein products which will physically make the repairs.
Cataracts
UV radiation also affects cells of the cornea and lens in the eye. When these cells experience prolonged exposure to UV-B radiation, cloudiness occurs in the normally translucent lens of the eye. Problems to the lens in the eye resulting from UV-B radiation are exacerbated in northern areas where snow reflects sunlight directly into the eye.
The damage that occurs is both acute and long-term. Momentary cloudiness occurs if you stare directly into the sun for a short period of time. Additive effects over time cause cataracts to form permanently.
Photoaging
Prolonged exposure to UV radiation from the sun causes photoaging. Photoaged skin looks wrinkled and leathery. This effect develops over time over time and is caused by breakdown of collagen in the skin. In the November 13, 1997 issue of New England Journal of Medicine, Gary Fisher, et.al., found a link between UV radiation and degradation of collagen due to enzymes called metalloproteinases.
Immunosuppression
UV radiation can affecting the immune system, causing immunosuppression in otherwise healthy skin cells. According to the World Health Organization, UV radiation can damage cells required to mount immune responses to infections. This damage can allow for opportunistic pathogens to infect their host, and for cancers to potentially develop.
References
- United States Environmental Protection Agency: UV Radiation
- Journal of Biomedicine and Biotechnology: A model for UV-induction of skin cancer
- New England Journal of Medicine: Pathophysiology of Premature Skin Aging Induced by Ultraviolet Light
- World Health Organization: Does UV Interact With The Immune System?
