There is no UV ray in winter, but be careful about getting sunburned!

As winter approaches, many friends will ask, the winter sun is not as strong as the summer sun, do we still need sunscreen?

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Before answering this question, the first thing we need to clarify is: What does sunscreen protect against ?

01

Ultraviolet rays - no protection

Sunscreen protects against ultraviolet rays, which can be divided into three wavelengths : UVA, UVB, and UVC :

1. UVA has the longest wavelength (320~400nm), which can penetrate the ozone layer and glass, reaching the dermis deep in the skin, causing the skin to tan and age.

2. The wavelength of UVB is shorter than that of UVA (290~320nm), which can penetrate the ozone layer to reach the ground and act on the epidermis of the skin, causing redness and sunburn.

3. UVC has the shortest wavelength (100~290nm) and weaker penetrating power. It is generally blocked by the earth's ozone layer and has no effect on the skin.

Therefore, whether to wear sunscreen does not depend on the season , but on whether the intensity of ultraviolet rays on that day reaches the level that requires sunscreen.

Generally speaking, ultraviolet rays are stronger in summer, and medium-wave ultraviolet rays UVB are less in winter, but winter and spring are the seasons with the lowest global ozone content in the year. Without the ozone layer, which is a "protective coat", more than 95% of the long-wave UVA ultraviolet rays in sunlight will penetrate the clouds. Therefore, sun protection is also needed in winter, and sunscreen needs to be used, but the SPF can be slightly lower.

02

If you don’t use sunscreen, beware of these 4 skin problems

Even so, there are still many friends who think sun protection is troublesome.

In recent years, with the advancement of science and technology and the improvement of living standards, people have paid more and more attention to the issue of facial rejuvenation. As the first barrier between the human body and the outside world, the skin is also the largest organ and one of the first parts of the human body to age. Skin aging is mainly divided into two forms: natural aging and photoaging . Among all the external factors that cause skin aging, ultraviolet rays are the most harmful. So, what damage does ultraviolet light cause to the skin?

1. Sunburn

If no sun protection measures are taken, the skin of ordinary yellow people will become sunburned after being exposed to strong sunlight for about 15 minutes. If they continue to be exposed to the sun, they will feel burning pain and even peeling.

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2. Tanning

When melanocytes are exposed to ultraviolet rays, they will accelerate the secretion of melanin, and the size of melanocytes will also increase, eventually causing the skin to darken. After tanning, it is not so easy to restore the skin to its pre-tanning state.

3. Photosensitivity

Some people are highly sensitive to ultraviolet rays and may have acute reactions after being exposed to ultraviolet rays. If they consume a large amount of photosensitive foods at this time, they may suffer from severe photosensitivity reactions under the induction of photosensitive ingredients. Symptoms include rash, exudation, erythema, itching, etc.

4. Sunbathing

Ultraviolet rays can damage collagen and elastin, abnormally thicken the stratum corneum, and reduce skin elasticity, moisture, and luster. Skin aging is even directly called "photoaging" . Compared with natural aging, photoaging is more likely to cause precancerous lesions, leathery appearance, and elastic tissue degeneration. Photoaging is manifested in loose and thickened skin with deep and coarse wrinkles. People who engage in outdoor activities for a long time can see diamond-shaped skin on their necks, with local pigmentation and capillary dilation, which looks "weathered". Sunlight not only causes skin aging, but can also cause a variety of skin diseases and easily cause various skin tumors, such as: solar keratosis, squamous cell carcinoma, melanocytoma, etc.

03

Sun protection tips: ABCD principle

Seeing this, we know that ultraviolet rays are the main external cause of human skin aging, so sun protection is very important. So how to protect yourself from the sun correctly? Next, let's talk about the ABCD principle of sun protection:

1. Sun protection principle A: Avoiding the sun is the best protection

No matter how strong the ultraviolet rays are, they cannot penetrate a wall. The best way to protect yourself from the sun is to avoid being exposed to the sun. You can avoid 60% or even more of the damage caused by ultraviolet rays by doing the following two things.

Avoid activities in the sun between 10:00 and 16:00. The strongest UV rays are from 12:00 to 14:00, and the intensity of UV rays decreases significantly after 16:00.

When going out, choose to walk or stay in cool places, such as under the shade of trees or under the eaves.

2. Sunscreen B principle: Hard sunscreen is preferred

Hard sun protection refers to a sun protection method that uses items such as umbrellas, hats, sunglasses, and clothing to block ultraviolet rays, visible light, and even infrared rays.

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3. Sunscreen C principle: Apply sunscreen when necessary

Avoid relying on sunscreen and reduce the burden on your skin, because no matter what ingredients the sunscreen is made of, it is more or less irritating, and some ingredients have relatively large side effects.

People with sensitive, damaged, or inflamed skin should be more cautious when choosing sunscreen products, because certain sunscreens are more likely to penetrate this type of skin and may cause photosensitivity reactions.

However, you must use sunscreen when necessary, such as: outdoor work, beach swimming, field hiking, plateau mountaineering, learning to drive in the summer, long-term sports under the scorching sun, insufficient hard sunscreen or inconvenient protection against ultraviolet rays, etc.

4. Sun protection principle: proper diet

Studies have found that taking antioxidants (such as vitamin C, vitamin E, vitamin B3, carotene, etc.) can reduce the damage caused by sunlight.

04

Learn to choose sunscreen correctly

In addition to adhering to the ABCD principles of sun protection in daily life, we also need to learn how to choose sunscreen correctly:

First of all, many people have discovered that there are two values ​​on sunscreen: SPF value and PA value . What do these two values ​​represent?

SPF is the sun protection factor, or sun protection multiple , which mainly refers to the product's protection index against medium-wave ultraviolet rays. The higher the SPF value, the stronger the protection against medium-wave ultraviolet rays. Each unit of the SPF value represents the ability to stay in the sun for 15 minutes without being harmed by UVB.

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For example, if erythema appears on the skin after 15 minutes of exposure to sunlight, after using sunscreen with a SPA of 20, the time when erythema appears on the skin can be extended to 15*20=300 minutes. In other words, the face that would turn red after 15 minutes can be protected by this sunscreen for 5 hours.

PA is the tanning index , which mainly refers to the product's protection index against long-wave ultraviolet rays, with "+" indicating the product's defense ability. The more "+" signs there are, the greater the PA value is, and the stronger the protection against long-wave ultraviolet rays is. Specifically, PA+ means that it can delay skin tanning by 2-4 times, PA++ means that it can delay it by 4-8 times, and PA+++ means that it can delay it by more than 8 times.

The sun protection ability of a sunscreen product is determined by the above two values.

If we are doing outdoor activities under normal sunlight, we can choose an index of SPF15. If we are doing exposed activities in places like strong light or beaches, we can choose sunscreen products with SPF of 30 to 50. Generally, we start applying sunscreen 15 to 20 minutes before exposure to sunlight. A coin-thick sunscreen can cover the entire face. However, under strong sunlight outdoors, you may sweat or rub off the sunscreen, so you need to reapply it every two hours to achieve a good sun protection effect.

Author: Wang Fang, attending physician of cosmetic dermatology, master of medicine

Reviewer: Li Feng, Director of Dermatology Department, Peking Union Medical College Hospital

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