What is SPF
The ultraviolet rays in sunlight can be divided into four kinds of rays according to different wavelengths, namely UVA, UVB, UVC and UVD. It is the longer-wave rays that can affect the health of human skin. Generally speaking, the ultraviolet rays that human skin needs to protect are UVA and UVB. The sun protection factor for UVA protection is expressed as PA or PPD, and the sun protection factor for UVB protection is expressed as SPF.
PA and PPD
UVA is long-wave ultraviolet, divided into UVA-1 (360-400nm) and UVA-2 (320-360nm), about It accounts for 10 percent to 20 percent. As long as UVA exists during the day, it can penetrate most of the clouds and glass and directly reach the dermis of the skin. Therefore, even on cloudy and rainy days, UVA rays will not decrease. It can reduce the content of hyaluronic acid bound to water in the skin, dry the skin, accelerate the formation of melanin, and darken the complexion. After reaching the dermis of the skin, it can destroy the collagen fibers and elastic fibers of the dermis of the skin, causing the skin to appear wrinkles and Aging is also an important cause of skin cancer.
The index of UVA protection is average Expressed in PPD or PA. PPD is a multiple of the time used by the European and American systems to prolong the time that the skin is tanned by UVA. Generally, after the skin is irradiated by ultraviolet UVA for 2 hours, the skin still tans continuously. Using PPD2 sunscreen can effectively protect UVA for up to 2 hours, and so on, which is the most practical protection factor to prevent dark spots. PA is a reflection of the effect of UVA tanning used by the Japanese system, and is expressed by the number of plus signs: PA+ = PPD 2-4, PA++ = PPD 4-8, PA+++ = PPD>8. That is to say, PA+ can protect UVA for 2 hours to 4 hours, and so on for every plus sign.
SPF
The redness of the skin after sun exposure, medically known as ‘erythema,’ is the mildest form of the skin’s response to sun exposure reaction. The minimum erythema dose is the shortest amount of sun exposure during which erythema appears on the skin. After using sunscreen, the skin’s minimum erythema dose will increase, then the sun protection factor SPF of the sunscreen is:
SPF=minimum erythema dose (after sunscreen)/minimum erythema dose (with sunscreen)
The SPF value applies to everyone and is calculated as: Assuming that the intensity of UV rays does not change over time, a person without any sun protection would be in the sun after 20 minutes The skin will turn red, and when he uses SPF15 sunscreen, it can be extended by 15 times, that is, the skin will be red after 300 minutes. SPF is a test index that measures the ability of sunscreens to protect against UVB rays in sunlight.
There is also an index PA. PA is the ‘UVA Prevention Effect Determination Standard’ announced by the Japan Cosmetics Industry Federation in 1996. It is the most widely used standard in Japanese products. The defense effect is divided into three levels, namely PA+, PA++, PA+++, and PA+ means effective. , PA++ means quite effective, PA+++ means very effective. The sun protection factor PA is a detection index that measures the defense ability of sunscreens against ultraviolet UVA in sunlight. For the PA value, there is no international certification standard.
Ultraviolet
The ultraviolet light in sunlight is invisible light, which is divided into 3 zones according to different wavelengths:
UVA zone , Long-wave ultraviolet rays, accounting for about 10 percent to 20 percent, it is the main reason for premature aging of the skin, can penetrate the dermis, tan the skin, and cause damage to lipids and collagen, causing photoaging of the skin and even Skin cancer, whose effects are slow and long-lasting, has a cumulative nature, so it is called ‘aging ultraviolet rays’ and is not blocked by windows, umbrellas, etc., even if it is cloudy and rainy.
UVB area, medium-wave ultraviolet, accounts for about 80 percent to 90 percent, it can reach the dermis layer, causing the skin to be sunburned, causing skin peeling, erythema, tanning and other phenomena, but it can be damaged by glass , umbrellas, clothes, etc.
UVC zone, short-wave ultraviolet, which cannot reach the ground because it is absorbed as it passes through the ozone layer.
The meaning of SPF 50 and 30
1. The meaning of SPF 50
SPF 50 generally refers to SPF50 means that it can protect from the sun for 750 minutes. Generally, if the human skin does not take sunscreen measures, it will usually appear red in 15 minutes in the sun, and the SPF 50 means that the sunscreen time of sunscreen can be extended by 50 times, that is to say, the use of sunscreen with an SPF of 50 The cream can be left in the sun for 750 minutes before it gets reddened.
2. The significance of SPF 30
SPF 30 refers to SPF30, which means that it can protect against sun for 450 minutes. In the same way, after applying SPF30 sunscreen, the human body can stay in the sun for 450 minutes before the skin becomes red.
Is the higher the sunscreen SPF the better?
Although SPF is an important indicator of sun protection, it does not mean that the higher the SPF value, the better the protection the stronger. For example, SPF15 has 93 percent protection ability, while SPF34 has only 79 percent protection ability. However, the larger the SPF value, the worse its permeability, which will hinder the normal secretion and respiration of the skin. According to the research of dermatology experts, in terms of the skin quality of oriental people, SPF10~SPF15 sunscreens can be used for daily protection; if you are engaged in outdoor leisure activities such as swimming and playing ball, SPF20 is enough to resist the damage of ultraviolet rays, and will not give the skin cause a burden. When we buy sunscreen products, we must read the instructions carefully, choose products with appropriate sun protection factor (SPF), and find out whether the products have UVA protection functions, so that you can buy the products you need.
According to the research of dermatologists, the most appropriate sun protection factor is between SPF15 and SPF30, because, in general, SPF15 products can block 93.3 percent of UVB, while SPF30 sunscreen The coefficient can withstand 96.6 percent of UVB. In addition, products with too high SPF are relatively greasy and heavy in texture, which can easily clog pores, and even breed acne and pimples. And some high-factor sunscreens that are chemical sunscreens will be converted into other substances after absorbing heat energy under the irradiation of long-wave ultraviolet rays, which will cause skin allergies. In addition to considering the sun protection factor, you may wish to look at the ingredients attached to it, or try it out first, and then make the final decision.
How to calculate SPF
Sun exposure can cause photoaging, dark spots, freckles, and more. Sunscreen products can effectively resist UVA and UVB damage to the skin. To find out how long a sunscreen protects you, you should first know how long you need to be in the sun without using sunscreen at all before your skin turns a little reddish; Then multiply the required time by the SPF value to get the protection time of the sunscreen. In other words, the SPF value marked on the sunscreen is the protection index it provides.
Example: If your skin turns slightly reddish after 20 minutes in the sun without sunscreen, an SPF 15 product will protect you for 5 hours as long as.
20 (minutes) * 15 (SPF) = 300 minutes (5 hours)
How to choose the sunscreen index in summer?
First of all, the sunscreen index in summer should be selected according to the environment. If you are just an ordinary office worker who usually works indoors and only gets sun exposure when commuting to and from get off work, then a sunscreen index of less than 15 is enough. If you are going to participate in outdoor activities, such as hiking or traveling, you can choose a sunscreen with an SPF of around 20. If you’re going to swim at the beach or open-air baths, choose a sunscreen with SPF 30.
Secondly, the choice of sunscreen index is also related to individual skin type. For example, if you have oily skin, you can choose some sunscreens with a lower SPF, such as SPF 15 or less, because the higher the SPF, the more greasy the sunscreen will be. If you have dry skin, you can choose a sunscreen with a slightly higher SPF level, such as around 20, which will not only protect against sun, but also effectively hydrate.
In addition, if it is sunny, the SPF can be higher. If it is cloudy, the SPF of the sunscreen should be kept within 15, and it should not be too high, so as not to block the sweat glands and cause skin allergies.
If you don’t know what skin type you are, experts here recommend a sunscreen for any skin type – Neutrogena Lightweight Sunscreen SPF30+. This sunscreen lotion is very lightweight and suitable for summer use. It is refreshing and non-greasy when applied on the face. The sunscreen and moisturizing effect is very good. It contains the patented formula Helioplex which absorbs UV rays so that the skin is protected from UV rays. Not only can it effectively sunscreen, but also moisturizing and whitening.
After choosing a good summer sunscreen index, the correct use of sunscreen is also very important. Sunscreen must be applied 15 minutes before going out, so that it can be absorbed by the skin when going out, and, in the process of going out, it should be applied every 2 hours to avoid the sunscreen effect of sunscreen being invalid. If you want to wipe the barrier cream, you must wipe the barrier first, and then apply the sunscreen.
How much SPF is appropriate
Using an SPF of 30 is usually enough. A sunscreen with an SPF of 50 is suitable for those who require prolonged exposure to the sun. You can use SPF 30 when you go out a little or don’t need to be exposed to the sun for a long time. If you don’t need to go out, you can use a sunscreen with an index of 15. In addition, people with fair skin can choose a sunscreen with an SPF of 30 or more to prevent spots from growing, and those with darker skin can use a sunscreen with an SPF of 15.
What is the right SPF for men?
How should men choose sunscreens? Men’s skin is different from women’s, so men choose sunscreen products, depending on their response to UV rays. If your skin is not very sensitive to UV rays, you can apply sunscreen with an SPF of 2-10 times. If your skin reacts strongly to UV rays, you can choose a high-strength sunscreen.
Men with sensitive skin to UV rays should rub it every 2-3 hours outdoors. If your skin is less sensitive to sunlight, you can rub it every other day. Also, if the altitude is high and the sun is strong, choose a sunscreen with a higher SPF.
What is the right SPF for men? Generally speaking, SPF10-20 in daily life is enough. If you go out, the SPF index can be appropriately higher. Of course, the choice of SPF index of sunscreen is also related to each person’s constitution. If your skin is sensitive to the sun, you should choose a high-power sunscreen. If you are not too sensitive, you can choose some low-power sunscreens.