What does it mean that sunscreen is waterproof? Do I need to reapply?

Many people know about sunscreen, which is applied on the face and can also be used on other parts of the body. So what does it mean that sunscreen is waterproof? Does waterproof sunscreen need to be reapplied?

What does it mean that sunscreen is waterproof?

The waterproofness of sunscreen refers to the waterproof effect of the sunscreen. Through the waterproof effect, you can see whether the sunscreen is suitable for use outdoors or at the beach. The more waterproof the sunscreen is, the more suitable it is for outdoor or beach use. If the sunscreen is not very waterproof, it is recommended to use it indoors or outdoors when it is not very hot.

Do I need to reapply waterproof sunscreen?

If the sunscreen you buy is waterproof, you still need to reapply it because the reapplication time of sunscreen is generally determined by the SPF value. The minimum erythema dose of human skin is generally 20 minutes, and the SPF value determines how many times the protection time can be increased. That is, assuming that the SPF value of your sunscreen is 15, the time it can protect against ultraviolet UVB is 20 times 15 = 300 minutes. If the SPF value is 30, then the time it can protect against ultraviolet UVB is 20 times 30 = 600 minutes. That is to say, the decision of whether girls should reapply sunscreen is not based on water resistance, but on the SPF value.

This is the end of the introduction to the issue of whether sunscreen is waterproof. It is still necessary to understand some common sense.