Most people know that we should do the sun protection no matter on sunny days and cloudy days. But there are still some people think that if there is no sun outside there is no need to apply sunscreen! Is it real? Can you say goodbye to sun protection on cloudy days? Here I share some knowledge of sun protection.
What are we defense from the sun protection is not the visible light, but the ultraviolet rays! The term ultraviolet light is familiar to everyone. According to physics, it is a general term for radiation in the electromagnetic spectrum from 10 nm to 400 nm. The human eye can not actually see it. Therefore, the main reason for our sun protection is these invisible radiations!
In fact, ultraviolet light is just a general term. The international name is UV. UV also contains UVC, UVA, UVB, and these are some of the terms we usually see on the description of sunscreen.
UVC: UVC is ultraviolet light having a wavelength of 200 to 290 nm. Short-wave ultraviolet rays are absorbed by the ozone layer when passing through the stratosphere on the surface of the earth, and cannot reach the surface of the earth. So the general sunscreen rarely mentions him.
UVB: ultraviolet light having a wavelength of 290 to 320 nm. Most of this UVB will be absorbed by the epidermis of our skin, which will cause strong photodamage to our skin, and the skin will appear redness, blisters and other symptoms. Long-term exposure to the skin will cause erythema, inflammation, skin aging, and severe cases can cause skin cancer.
UVA: UV light with a wavelength of 320~400nm. This long-wave UV is more penetrating to clothing and human skin than UVB, and he can even reach our dermis. Long-term exposure to this kind of ultraviolet light causes the precipitation of melanin in our skin, which makes us black.
The SPF value is used to reflect the protection against UVB. SPF = minimum erythema dose (after sunscreen) / minimum erythema dose (before sunscreen) The minimum erythema dose is the shortest sun exposure time for erythema on the skin. So this value actually tells us that a sunscreen labeled SPF20 can theoretically prolong the time to produce erythema by 20 times.
The UVA protection label should be PFA (protection factor of UVA), the calculation method is similar to SPF, PFA = skin blackening (after sunscreen) / skin blackening (before sunscreen), meaning a PFA value of 5 Sunscreen products can increase the skin's ability to withstand UVA by a factor of five.
However, there is no uniform regulation on the UVA protection of the sunscreen bottle in various countries. In Asia, we mainly use the PA mark. PFA values below 2 to 3 are expressed as PA+, 4 to 7 are expressed as PA++, and 8 or more are expressed as PA+++. In Europe, the main use of "Boots Star Rating" to mark, there are 3 levels, from 3 stars to 5 stars.
1. When choosing a sunscreen product, please choose the lotion and creamy texture. Sunscreen sprays should be used primarily for refilling because spray-type sunscreens are not easy to apply evenly.
2, sunscreen is not painted once and for all, you need to apply regularly! Through the above introduction, you can find that the protection of UV rays from UV rays is related to the length of time. Therefore, if you need to be exposed to the sun for a long time, you must bring a bottle of sunscreen products for recoating.
3, do not lick your sunscreen, be sure to apply enough. Because we have oil and sweat when we are outdoors, it also weakens the protection of sunscreen to some extent.
4. At present, weather stations in major cities have an index for measuring daily ultraviolet rays. Please pay attention to the sunscreen according to the tips.
5, SPF value and PA value are not the higher the better, the most important thing is to choose the appropriate sunscreen according to the environment you are in, not to burden the skin, but also to achieve the sunscreen effect. Generally, the indoor use SPF value is 15-20, PA++ is enough. When going out, choose SPF value greater than 20, PA+++, go to the beach and recommend SPF30, PA+++.
Now have you understand that we should do sun protection work every day? If we do not apply the sunscreen. It can stimulate the synthesis of pigments and cause the skin to "blacken up", leading to the appearance or aggravation of freckles, chloasma, and age spots. Hurry up and do sun protection.