Did you know that sun protection not only protects against UVB rays, but also UVA?
There are two kinds of ultraviolet light: UVB and UVA. UVA band, wavelength 320 ~ 400nm, also known as long wave black spot effect ultraviolet. UVB (English full name: ultraviolet radiation b) is a band divided into ultraviolet wavelengths according to different biological effects. UVB is outdoor ultraviolet radiation, which is directly injected into the skin when people are outdoors.
Initially, sunscreen products were designed to prevent sunburn caused by UVB, but less attention was paid to UVA protection. With the development of the sunscreen product market and the continuous in-depth research on UV protection, the importance and necessity of UVA protection is constantly increasing.
UVB damage and protection has been thoroughly studied, it can make the skin in a short time of sunburn, sunburn (for the average person is about 25 minutes), the vast majority of sunscreens on the market are UVB type, SPF is the symbol of UVB protection ability.
The SPF value refers to the ability of the product to protect against UVB rays, which is the ability to prevent the skin from getting red and sunburned. Generally speaking, the time for human skin to produce red spots in direct sunlight is 20-25 minutes, if the SPF value of a bottle of sunscreen is 8, apply it once, the protection time of the skin is 20 (25) ×8=160 (200) minutes.
UVA is a terrible sun killer. With its long wavelength and strong penetrating ability, it can penetrate the surface layer of the skin and penetrate deep into the tissues below the dermis. It can destroy the fine structures inside the skin such as collagen and elastic fiber tissue, resulting in wrinkles and fine lines, and make the skin loose and aging. This is medically known as photoaging.
In the energy distribution of ultraviolet rays in sunlight, UVA is 15 times that of UVB, which is the main cause of skin tanning. It can reduce the content of hyaluronic acid in the skin that binds water, dry the skin, accelerate the formation of melanin, darken the skin, and is also an important cause of skin cancer.
It has been found that the general intensity of sunlight UVA irradiation on the skin, after about 2-4 hours, the skin will appear relatively stable blackening, academically called "continuous instant blackening".
In addition to the SPF number, you can often find the word "PA+" on the packaging of sunscreen products, which indicates the ability of the product to protect against UVA, that is, the ability to prevent suntanning. Generally, the products with this logo are just launched sunscreen products, which are relatively advanced in technology.
Broad-spectrum sunscreen products refer to sunscreen cosmetics that can block both the A-band (UVA, 315-400nm) and the B-band (UVB, 280-315nm) in the two areas of the sun's rays, in order to protect the skin from the adverse effects caused by ultraviolet rays.