Recently, Wang Baoxi, chief physician of Plastic Surgery Hospital of China Academy of Medical Sciences, said in the live broadcast of popular science consultation on the client of "People's Good Doctor" that unopened sunscreen can still be used normally within the validity period as long as it is well sealed and properly preserved. "For the sunscreen that has been used, after another year, the matrix inside may have changed, and it is not recommended to continue using it.
As for sun protection time, office sun protection: If you stay indoors most of the time, SPF 15 PA+ sun protection is enough. Apply it again every 4-5 hours.
Sunscreen for outdoor sports: If you go out for sports, you should use SPF25-30 PA++ sunscreen and replenish it every 3-4 hours.
Sunscreen when swimming: It is best to choose waterproof sunscreen when swimming, and use SPF above 30 Pa+++, and rub it once every 1-2 hours.
Extended data:
Five misunderstandings of sun protection that should be avoided
Myth 1: Apply sunscreen every two hours without exception.
There are many versions on the Internet about how often to apply sunscreen, and the most popular one is to apply sunscreen every two hours. In fact, it depends on different sun protection needs, and different SPF values have different sun protection time, so two hours can't be used as the standard for touch-up.
Office sun protection: If you stay indoors most of the time, SPF 15 PA+ sunscreen is enough. Apply it again every 4-5 hours.
Sunscreen for outdoor sports: If you go out for sports, you should use SPF25-30 PA++ sunscreen and replenish it every 3-4 hours.
Sunscreen when swimming: It is best to choose waterproof sunscreen when swimming, and use SPF above 30 Pa+++, and rub it once every 1-2 hours.
Myth 2: Applying sunscreen products can produce sunscreen effect immediately.
Many MM wear sunscreen to go out, and when they get tanned, they blame the sunscreen for not working. Actually, it's all your own fault! Because the effective ingredients in sunscreen must penetrate into the cutin surface layer, it can play a long-term protective role. So it is necessary to wipe it 30 minutes before going out and make it up again before going out. In terms of dosage, it should be at least 1~2 ml each time to achieve the best sunscreen effect.
Myth 3: It doesn't matter if you don't wear sunscreen occasionally.
Sometimes I feel lucky because I am lazy and don't wear sunscreen. I think it doesn't matter if I apply it once or twice. This is also a big mistake. You should know that exposure can be accumulated, and indirect exposure may not be a problem for the time being, but after a long time, it will cause tanning, spots on the face, skin loss of elasticity, wrinkles and aging. Therefore, you should not be lazy about sunscreen, and you must adhere to the good habit of applying sunscreen products as much as possible.
Myth 4: The higher the sun protection index, the better the sun protection effect.
The higher the SPF, the more sunscreen added to this product, and the greater the irritation to the skin. Therefore, it will feel uncomfortable after wearing it and is not suitable for daily use. The correct way is to choose products with different SPF according to different requirements of different occasions. Then it came out, and you can "fight the world" with only one sunscreen. Everyone should have at least three different SPF sunscreen products.
Myth 5: The skin has been tanned, and it is useless to apply sunscreen.
Don't take such a self-destructive attitude towards sun protection. When the skin turns brown after sun exposure, it will become self-protective, and the thickening of the skin and the production of melanin will protect the skin. However, melanin can still absorb some ultraviolet rays. Long-term exposure to melanin will aggregate to form spots and even cause skin cancer. Therefore, apply sunscreen outdoors to prevent skin damage.
References:
People's health network-sunscreen
People's Network-Sunscreen