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The sunscreen industry markets its products with SPF (Sun Protection Factor) ratings. Sunscreen products of various SPF ratings will be tested for their UV absorbance and effectiveness.Earth's atmosphere prevents mostultraviolet (UV) radiation given off by the Sun from reaching the ground. The radiation tends to be screened out bystratospheric ozone, which is about 35 km above the Earth's surface. UV radiation has both positive and negative effects. Positive effects of UV radiation include warmth, light, photosynthesis in plants, and vitamin D synthesis in the human body. However, too much exposure to UV damages skin cellsand leads to wrinkled and patchy skin, cataracts, and even skin cancer.Ultraviolet (UV) radiation is often divided into three different ranges:UV-A, UV-B, and UV-C. UV-A radiation constitutes about 90-95% of the UV radiation that reaches the Earth's surface and can penetrate deeply into the skin, leading to premature skin aging and cancer. UV-B radiation does not penetrate the skin as far as UV-A rays, but itcontains much more energy. UV-B is involved in tanning and sunburn, and can cause cellular damage inthe skin and eyes. UV-C radiation has the highest energy ultraviolet wavelength, but most of it is absorbed by the ozone layer in the Earth's upper atmosphere.When the human skin absorbs UV radiation, two effects occur. First, melanin (a substance located in skin cells) absorbs as much UV radiation as possible and is changed to a darker color. The second effect is the destruction of the cells responsible for making new cells, or even worse, a rearrangement or chemical change in the DNA within these cells. If these special cells are destroyed, the nervous system sensors are also damaged resulting in pain and increase in the blood circulation in the area, producing the characteristic red skin of sunburn.
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Fecha publicación: 12.5.2016
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