Detailed explanation: SPF

Redness of the skin after sun exposure is medically known as “erythema”, which is a mild reaction of the skin to sun exposure. A low erythema dose is a short period of sun exposure during which erythema appears on the skin. After using sunscreen products, the low erythema dose of the skin will increase, then the sun protection factor SPF of the sunscreen product is:

SPF=low erythema dose (after using sunscreen)/low erythema dose (before using sunscreen)

The value of SPF sun protection factor is applicable to everyone. The calculation method is: assuming that the intensity of ultraviolet rays does not change over time, a person without any sun protection measures will turn red after staying in the sun for 20 minutes. When he uses SPF15 When using sunscreen, it means that the time can be extended 15 times, that is, the skin will not become red after 300 minutes. Sun protection factor SPF is a test index that measures the ability of sunscreen products to protect against UVB ultraviolet rays in the sun.

There is also an index PA. PA is the “UVA prevention effect measurement standard” announced by the Japan Cosmetics Industry Federation in 1996. It is currently a widely adopted standard for Japanese products. The defense effect is divided into three levels, namely PA+, PA++, PA+++, PA+ means effective, PA++ means quite effective, PA+++ means very effective. Sun protection factor PA is a test index that measures the ability of sunscreen products to protect against UVA rays in the sun. For PA value, there is no international certification standard.