What is the principle of sunscreen?

Sunscreen is divided into physical sunscreen and chemical sunscreen, which are explained separately below:

1. Physical sunscreen: Using the principles of physics, the atomic particles of this sunscreen are flakes. It uses reflective particles, such as titanium dioxide and zinc oxide, to reflect and scatter light, reducing the amount of ultraviolet rays reaching the skin to achieve the purpose of sun protection.

2. Chemical sunscreen: Sunscreen is achieved by absorbing harmful ultraviolet rays. Since chemical sunscreen molecules are absorbed by the skin, the process of absorbing ultraviolet rays occurs inside the skin and is metabolized and eliminated by the body. Extended information

The meaning of SPF and PA+ on sunscreen

SPF value: Also known as sun protection factor, it is an evaluation index of the protective effect of sunscreen on ultraviolet rays (UVB). Red spots will appear on the skin after being exposed to medium-wave ultraviolet rays for a certain period of time. After using sunscreen, erythema will not appear, but if the exposure time is extended, the same degree of erythema will appear. This extended time is the protective effect of sunscreen.

According to the "Hygienic Standards for Cosmetics" officially implemented in my country on July 1, 2007, when the SPF value of the measured sunscreen cosmetic product is higher than 30, and it is still greater than 30 after subtracting the standard deviation, the maximum Only SPF3 can be marked, not the actual measured value.

PA value: Indicates the protective effect of sunscreen products on long-wave ultraviolet rays (UVA). The short-term biological effect of UVA exposure is skin tanning, and the long-term cumulative effect is skin aging. The more “+”s in PA, the better the effect against UVA.

Baidu Encyclopedia-Sunscreen Lotion

Baidu Encyclopedia-SPF