On October 27 2017, the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization was initially compiled for reference. Ultraviolet radiation (wavelength 100-400 nm, including UVA, UVB and UVC) was included in the list of a category of carcinogens.
What is the so-called sun protection? The answer is ‘Ultraviolet rays’.
The two parameters of SPF and PA represent the level of UV protection of a certain sunscreen product. Among them, SPF refers to the ability to defend against Ultraviolet B (UVB), and PA refers to the ability to defend against long wave Ultraviolet A (UVA). These two kinds of ultraviolet rays are the main cause of damage to human skin in sunlight.
The difference between UVB and UVA and the principle of effect on the skin is that UVA can penetrate the dermis of the skin and are the main cause for skin darkening. Long-term sun exposure can accelerate skin aging and even cause skin cancer. UVB can penetrate the epidermis of the skin and are the cause of skin damage (sunburn, erythema, edema, pain and even blisters).
Qualified sunscreens on the market will be marked with SPF and PA parameters. SPF refers to the ability to defend against UVB. Common parameters include SPF15+, SPF30+, SPF50+, etc. PA refers to the ability to defend against UVA, followed by a "+" sign.
Because UVB is very powerful in causing the skin to be sun-burnt, for a long time sunscreen products only focused on UVB protection However later scientists discovered the damage of UVA to the skin, related sunscreens and products to prevent UVA were slowly developed. So now regular sunscreen products will be marked with SPF and PA at the same time.
The value behind SPF means that how long the product can prolong the time of one being sun-burnt. Under normal circumstances, 15 minutes in direct sunlight will cause damage, therefore, SPF15+, SPF30+, SPF50+, etc. means that sunscreen products have about 225 minutes (15 minutes × 15, about 3.5 hours), 450 minutes (15 minutes × 30, about 7.5 hours), and 750 minutes (15 minutes × 50, About 12.5 hours) sun protection time.
In short, the higher the value of SPF, the stronger the product's anti-UV effect. For example, the defense ability of SPF50+ is stronger than that of SPF15+. It can also be understood that SPF50+ has a longer sun protection time than SPF15+.
In this way, you can choose a sunscreen product with an appropriate sun protection factor according to different occasions and needs.
Similarly, the more "+" signs follow the PA, the better the protection against long-wave ultraviolet rays, and the less likely to be tanned and photo-aging.
PA++: quite effective
PA+++: very effective
How to choose sunscreen/sunscreen spray?
Sunscreens with low SPF values have fewer chemical components and are thinner and more comfortable to use. Therefore, when choosing sunscreen, it is not recommended to blindly pursue products with high SPF value. The sensible approach is to choose a suitable sunscreen product according to the needs and occasions of use.
In addition, sunscreen should be applied 15 minutes before going out, because sunscreen will only take effect 15 minutes after application. All parts of the body should be applied, especially in areas with strong ultraviolet rays. The back of the hands, neck, arms, forehead, etc. are all important areas.
Hopefully this article will give you some idea on how to choose your sun protection products. Remember, be smart about sun care and enjoy the sunny days!