Light can be divided into ultraviolet, infrared , visible light three parts and can be divided into ultraviolet UVA, UVB, UVC three parts. Because the shorter wavelength UVC which , already in the atmosphere by the ozone layer to the absorption, scattering out, so I can not reach the ground ranks among the three UVB wavelength , the wavelength can only reach the skin's epidermis and the longer wavelength UVA, will go into skin deep dermal layer of skin damage , causing skin aging.
UV is fired Earth from the sun in the UV spectrum part of its shorter wavelength than visible light , so that the naked eye can not see . According to the different wavelengths , UV can be divided into UVA, UVB , and UVC. UVA has the longest wavelength which reach 320-400 nm , UVB wavelength of 290-320 nm, and UVC is reaching the earth absorbed by the ozone layer before it . Is not absorbed by the ozone layer of UVA and UVB radiation to the earth's surface will be to bring harm to our skin , premature aging of the skin , caused damage to the eyes and even cause skin cancer. While they suppress the immune system weakening you against other diseases.
UVA ultraviolet light of life , through the window glass and clouds injections person's skin , most of the time of our lives exposed to UVA light under , he occupied all UV rays to reach the Earth 's 95% , although it did UVB so strong, but as long as there is sunshine, it will always exist , and to maintain a balanced strength , so we should pay attention all year round protection UVA.
UVA sun is terrible killer, it is by relatively long wavelength , penetrating ability of the skills that can penetrate the skin surface, deep dermis following organizations that can damage collagen, elastin fibers within the skin tissue and other fine structure , resulting in wrinkles and fine lines , skin laxity aging. Which is medically known as light-induced aging.
In the sun's ultraviolet energy distribution , UVA UVB is 15 times , is the main reason for skin tanning . It can make the skin 's hyaluronic acid bound water content decreases , the skin dry, accelerate the formation of melanin , the color black , is also an important reason to cause skin cancer .
It was found that the general strength of the sun UVA irradiation on the skin, after about 2-4 hours , the skin will appear more stable blackening academic called " persistent Instant blackening ."
UVB ultraviolet rays outdoors , people in outdoor activities directly into the skin. It is the skin to become red , the most important reason to be tan , it is more harmful to the skin surface of the main part , it is also the skin spots , aging and cause skin cancer culprit. However, the intensity of UVB place and over time in the changing seasons , UVB rays are the most intense time of April each year to 10 months of daily 10:00 to 16:00 , but it can hurt the skin all year round , especially at high altitudes . And after being reflected by snow or ice , and 80% of UVB is reflected back to secondary damage on the skin .
UVB damage and protection have been thoroughly studied , which can make the skin sunburn in a short , red sun ( the average person is 25 minutes or so ) , now on the market is the vast majority of UVB -type sunscreen , SPF is UVB protection logo.
The so-called SPF value refers to the product 's ability to UVB protection , that is, to prevent skin drying red sunburn capabilities. In general , human skin erythema in direct sunlight was 20-25 minutes , if the bottle is 8 SPF sunscreen , it is applied once the skin guard time is 20 (25) × 8 = 160 ( 200 ) minutes. Specifically refer to the following table:
Conditions of Use SPF value
2-8 winter sun , spring evening sunshine and rainy days
9-20 Summer evening sunshine and moderate intensity
21-30 working outdoors , travel, summer strong sunlight
Greater than 30 under certain circumstances ( such as high altitude ) , strong sunlight
In other countries, focus on UVA sunscreen SPF value on the package in addition to signs outside , can often be found "PA +" the words, they represent the product 's ability to UVA protection , which is the ability to prevent sunburn . Generally have this identification of the products are available sunscreen just technically more advanced, the current domestic products only Infinitus ( China ) Co., Ltd. " Rialto Ultra Care Sunscreen SPF30 + / PA + +" in this sign.
PA values correspond to the meaning of the index is as follows:
PA values effective protection time
PA + about 4 hours
PA + + for about 8 hours
PA + + + super protection