Sunscreens in other countries should be marked with PA value. If the PA value is not marked, it means that this sunscreen really has no effect on preventing A ultraviolet rays, or the brand is very amateur.
Extended data:
The original sunscreen only protects against uvb, because uvb can make people black. Later, it was found that light can also cause skin aging, so there was the pa index.
American medical scientists believe that spf 15=pa+. Secondly, the general view is that uva cannot be protected without pa. For example, in the United States, only SPF values are generally marked, but in recent years, two values will be marked at the same time internationally. Ppd index is the index that marks the defense against uva, and ppd8=pa++. In fact, the most accurate indicator is ppd index, such as sunscreen in la roche-posay.
Studies have shown that most skin cancers occur in the basal layer of epidermis. UVA can damage skin cells called keratinocytes in the basal layer of epidermis, which contributes to and may even directly lead to the generation and deterioration of skin cancer.
UVA can damage the collagen of the skin. The damage of collagen leads to the abnormal increase of elastin, which promotes the production of metalloproteinases and is used to repair damaged collagen. The incorrect repair of collagen by metalloproteinases makes the skin rough and leads to wrinkles. Because the skin is exposed to UVA rays every day, this process is repeated.
UVA protection factor? The abbreviation of, with numbers representing the ability of products to defend against UVA.
The test principle of this method is the same as SPF anthropometry, except that the ultraviolet band used in the test is UVA (wavelength range is 320-400nm). The ratio of the ultraviolet dose of skin with sunscreen to skin without sunscreen to produce the smallest erythema is the APF value.
References:
Baidu encyclopedia UVA