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This process of absorption works to reduce the risk of DNA damage and the formation of pyrimidine dimers. UVA light makes up 95% of the UV light that reaches earth, whereas UVB light makes up only about 5%. UVB light is the form of UV light that is responsible for tanning and burning. Sunscreens work to protect from both UVA and UVB rays.
UV light, specifically non-ionizing shorter-wavelength radiation such as UVC and UVB, causes direct DNA damage by initiating a synthesis reaction between two thymine molecules. The resulting dimer is very stable. Although they can be removed through excision repairs, when UV damage is extensive, the entire DNA molecule breaks down and the cell ...
Monoadduct damage cause by change in single nitrogenous base of DNA; Di adduct damage; Damage caused by exogenous agents comes in many forms. Some examples are: UV-B light causes crosslinking between adjacent cytosine and thymine bases creating pyrimidine dimers. This is called direct DNA damage. UV-A light creates mostly free radicals.
Prolonged optical exposure to sunlight, especially intense ultraviolet light, may be linked to cortical cataracts, [50] [15] and high levels of visible light is maybe linked to macular degeneration. However, significant daily exposure to bright light may be necessary for children to avoid myopia (nearsightedness). [51]
Indirect DNA damage: The chromophore absorbs UV-light (* denotes an excited state), and the energy of the excited state is creating singlet oxygen (1 O 2) or a hydroxyl radical (•OH), which then damages DNA through oxidation. [1]
Particular medications make the skin more sensitive to sunlight; these include most of the tetracycline antibiotics, heart drugs amiodarone, and sulfonamides. Some dietary supplements, such as St. John's Wort, include photosensitivity as a possible side effect. Particular conditions lead to increased light sensitivity.
One cause of cataracts is exposure to ultraviolet light. Provided the level of UV emission from lamps is within safe limits, and the lamp a sufficient distance away from the individual, there should be no increased risk of developing cataracts. Photophobia is a symptom of excessive sensitivity to light which affects 5 to 20% of the population ...
UV-B, predominantly responsible for the harmful effects of sunlight, poses the highest risk for erythema, photokeratitis, sunburn and skin cancer. [14] [15] [16] While longer UV-C wavelengths and UV-A can also cause damage, their effects are less severe than UV-B. In contrast, far-UVC has shown remarkably different results.