The UVA band is part of the ultraviolet wavelength division, with a wavelength of 320 to 420nm, also known as long-wave dark spot effect ultraviolet. It has strong penetrating power. UVA can directly reach the dermis layer of the skin, destroy elastic fibers and collagen fibers, and tan the skin.
UVA is a terrible sun killer. With its relatively long wavelength and strong penetrating ability, it can penetrate the surface of the skin and penetrate deeply into the tissues below the dermis. It can destroy the fine structures inside the skin such as collagen and elastic fiber tissue, causing wrinkles and wrinkles. Fine lines, sagging and aging skin. This is called photoaging in medicine.
In the energy distribution of ultraviolet rays in sunlight, UVA is 15 times more powerful than UVB and is the main cause of skin tanning. It can reduce the content of water-binding hyaluronic acid in the skin, dry the skin, accelerate the formation of melanin, and darken the skin color. It is also an important cause of skin cancer. The ozone layer can block and weaken ultraviolet rays.
PPD is a method used by European and American systems to refer to the multiple that prolongs the time the skin is tanned by UVA to represent long-term tanning. The tanning of the skin still persists after 2 hours of UVA exposure. It is a protection factor that is consistent with the actual prevention of dark spots. PPD can reflect the long-term tanning effect of sunscreen products on UVA. PA is the Japanese system used to reflect the UVA tanning effect, which is expressed by the number of plus signs:
PA+=PPD2-4
PA++=PPD4-8
PA+++=PPD>8
When buying sunscreen, pay attention to the SPF value, which protects against UVB rays. The higher the SPF value, the better. The higher the SPF value, the more difficult it is for the skin to “breathe”. When choosing sunscreen, you should also pay attention to protecting against UVA rays. The protection against this ray is represented by PA. The more plus signs, the better the sunscreen effect. At the same time, it is recommended to apply sunscreen 15 minutes before going out, because sunscreen does not take effect until 15 minutes after application. It should be applied to all parts of the body, especially in areas with strong UV rays. Apply sunscreen on the back of your hands, sprinkle it with water, and pick the one that can form water droplets.
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