It's these two guys that make waves on the skin: ultraviolet A (UVA) and ultraviolet B (UVB).
UVA: Wavelength 320nm-400nm, it can reach the dermis, indirectly damage DNA, promote photoaging, affect pigmentation, and may be involved in skin cancer.
UVB: With a wavelength of 290nm to 320nm, it can pass through the stratum corneum and epidermis, directly causing DNA damage, sunburn, inflammation, hyperpigmentation and photocarcinogenesis.
See here, know why we again and again emphasize the sun protection. In order to avoid UV attack on the skin, we need to use a variety of sunscreen "weapons" defense, sunscreen is one of the classic means.
The effective ingredients of each sunscreen are different, and some sunscreen must penetrate into the cuticle of the skin, or form the refraction film, so that the anti-suntan cream must be wiped 20 to 30 minutes before going out, in order to play the protective role.
The UVA in ultraviolet rays also exists in cloudy days. Even if the cloud is thick, it can hardly play any shielding role for ultraviolet rays. Therefore, even if you go out on cloudy days, you should also do a good job of sunscreen work in advance.
In fact, one application of sunscreen won't protect you for the whole day, since it tends to wash off when you sweat.
It is generally recommended to reapply once every 2 to 3 hours. Sunscreen takes about 30 minutes to take effect after you apply it, so apply it well in advance before going out.
Sunscreen the size of a $1 coin is recommended to protect the face from UV rays. If it is a hot day, reapply after 60 minutes.
Not all umbrellas have SPF. Even if it did, it would only block direct UV rays, not UV rays reflected off the ground. So wear sunscreen when you go out.
Although SPF is an important indicator of sun protection, it doesn't mean that the higher the SPF, the better the protection. The higher the SPF, the less permeable it is and the greater the burden on the skin.
It is usually recommended that people do not often outdoor activities, SPF15 or so is enough; If you do a lot of outdoor activities, you can use SPF15-30; If you go to areas with strong UV rays such as snowy mountains, plateaus, or beaches, you should use an SPF50+ sunscreen.
Even if we wear sunscreen, it doesn't affect how our bodies make vitamin D. For kids, don't go for a very high SPF, go for a high PA.
Sun exposure is cumulative, and the damage to the skin accumulates over time. You can't immediately see the effects of the sun, but over time you will tan and age.
If you have been tanned, if not remedied, the skin may tan and burn again, accelerating aging.
By the way, someone asked: Can you still use the sunscreen you opened last year? If the following 4 conditions occur, you should consider discontinuing use.
1. It is overdue. 2. It feels uncomfortable after applying it; 3. Changes in sunscreen properties, such as layering; 4. It smells funny.
