Sunscreen is a specialized lotion, spray, gel, cream, foam, or other topical product that absorbs or reflects some of the sun's ultraviolet (UV) radiation and thus helps prevent sunburn. Using sunscreen wisely can also slow or temporarily prevent the development of wrinkles and dark spots on the skin.
Depending on the mode of action, sunscreens can be classified into physical sunscreens (for example, zinc oxide and titanium dioxide, which remain on the skin's surface and mainly reflect ultraviolet radiation) or chemical sunscreens (for example, organic UV filters that absorb ultraviolet radiation). shine).
Sunscreens are usually rated and labeled with a sun protection factor (SPF), which measures the proportion of the total amount of UV radiation that gets on the skin. For example, "SPF 15" means that only 1/15 of the total radiation intensity reaches the skin through the recommended sunscreen thickness.
The sun protection factor (SPF rating introduced in 1974) is a measure of the proportion of ultraviolet rays (causing sunburn) that reaches the skin. For example, "SPF 15" means that only 1/15 of all radiation will reach the skin, provided sunscreen is applied evenly at 2 mg per square centimeter. The user can determine the effectiveness of sunscreen by multiplying the SPF by the time it takes him or her to burn without sunscreen. Thus, if a person develops a sunburn within 10 minutes without using sunscreen, then the same person with the same intensity of sunlight will take 150 minutes to develop a sunburn of the same severity with SPF 15 sunscreen. It should be noted that sunscreens with higher SPF are no longer effective or effective on the skin than creams with lower SPF, so they must be applied consistently as directed - usually every two hours.
SPF is an imperfect parameter for measuring skin damage because invisible skin damage and aging is also caused by UVA radiation (wavelength ~ 315-400 nm), which generally does not cause redness or pain. Conventional sunscreen blocks very little UVA radiation relative to the nominal SPF; broad spectrum sunscreens are designed to protect against UVA and UVB types. According to a 2004 study, UVA also causes DNA damage deep in the skin, increasing the risk of malignant melanomas. Even some products labeled “broad spectrum UVA / UVB protection” did not always provide good UV protection. Titanium dioxide probably provides good protection, but does not fully cover the UVA spectrum. Studies in the early 2000s show that zinc oxide is superior to titanium dioxide at wavelengths of 340–380 nm.