Do you only need to apply sunscreen once before going out?

That is not the case.

The main function of sunscreen is to block the damage of ultraviolet rays to the skin, which can reduce the risk of tanning, sunburn, photoaging and skin cancer. However, sunscreen is not a permanent solution, and its effectiveness can be reduced due to a variety of factors.

For example, prolonged outdoor activities, sweating, swimming or wiping sweat will reduce the coverage and effectiveness of sunscreen. In other words, the protective effect of sunscreen will gradually weaken over time, sweat, friction and other factors.

Therefore, even if you apply sunscreen before going out, you still need to reapply it regularly during outdoor activities to maintain its sun protection effect.

Generally speaking, sunscreen provides protection for about 2 hours, after which its effectiveness decreases significantly. Therefore, reapply sunscreen every 2 hours when outdoors to ensure continued effective protection. In addition, if you swim or sweat a lot, it is recommended to reapply sunscreen immediately after each activity.

In addition, if sunscreen is combined with physical sun protection measures such as long-sleeved clothing and sun hats, it can more effectively protect the skin from UV damage.

Author: Tang Jiaoqing, MD, attending physician of dermatology

Review | Feng Jun, deputy chief physician of the Dermatology Department of Sinopharm Tongmei General Hospital