Is it necessary to apply sunscreen even on cloudy days?

Review expert: Zhang Yuhong, chief physician of the Department of Dermatology, Zhengzhou Central Hospital Affiliated to Zhengzhou University

As summer approaches, many people begin to use various sunscreen products to prevent darkening and protect their skin.

However, when I was looking for sun protection tips, I saw some netizens who not only apply sun protection "all year round", but also apply sunscreen indoors. Is sun protection that important? Do you need sun protection even on cloudy days? Let's take a look.

1

How important is sun protection?

Some people may think that sunscreen is only needed in sunny weather and that it is too exaggerated to use sunscreen all year round. In fact, sunscreen is necessary regardless of whether it is sunny or cloudy.

Sunscreen does not protect against sunlight, but the invisible ultraviolet rays in sunlight. Ultraviolet rays refer to solar radiation with a wavelength range of 100nm to 400nm in the solar spectrum, including UVA (long wave), UVB (medium wave), and UVC (short wave).

Short-wave UVC is generally intercepted in the atmosphere, and only UVA and UVB can reach the earth's surface and directly hit human skin. Among them, the intensity of medium-wave ultraviolet light UVB (wavelength 280-315nm) is affected by the season, time, and environment. The damage to the skin remains in the epidermis, but it will be blocked by more clouds on cloudy days.

Long-wave ultraviolet light UVA (wavelength 315-400nm) has strong penetrating power and can penetrate clouds and glass and enter the dermis of the skin.

Image source: GB/T36744-2018

UV Index Forecast Method When exposed to ultraviolet rays, a large amount of pigment will be synthesized on the surface of the skin to resist radiation, so the skin will become darker. Appropriate exposure is beneficial, but long-term exposure may damage the skin's protective barrier, dry the skin, and produce wrinkles.

Image source: Baidu Encyclopedia

Moreover, if the skin is exposed to the midday sun for several hours, the blood vessels on its surface will dilate and become congested, forming large areas of erythema, making people feel burning and painful skin, leading to sunburn.

If you are exposed to the sun for a long time, there will be risks such as cataracts or chronic eye inflammation, and in severe cases, skin cancer . Therefore, the main purpose of sun protection is to prevent skin damage and other diseases caused by it.

The intensity of ultraviolet radiation can be measured by the UV index. The higher the index, the greater the damage to the skin, and corresponding sun protection measures need to be taken.

Image source: GB/T36744-2018

UV index forecasting method According to data from the China Meteorological Administration, although the annual UV amount reaches a peak from May to August, the amount of UV in winter is also not small, accounting for 1/3 of that in summer. Therefore, it is not unreasonable to carry out sun protection "all year round", especially in summer, sun protection measures are essential.

2

Sun protection tips revealed

The best way to protect yourself from the sun is to avoid being exposed to the sun. As long as you don't go out at noon or stay in the shade when you go out, you can reduce ultraviolet radiation to a great extent. But going out is always unavoidable, so you need to use "blocking the sun" and "applying sunscreen".

Image source: pixabay

"Blocking and sun protection" means using umbrellas, hats, sunglasses, sun-protective clothing and other external objects to block the skin, so that ultraviolet radiation and other radiation cannot directly contact the skin, effectively resisting ultraviolet radiation. "Blocking and sun protection" is effective, but it is inconvenient to carry when going out, and it is not possible to block the whole body. Some ultraviolet rays can be reflected by the ground and other factors onto the exposed skin.

"Applying sunscreen" refers to applying sunscreen, which includes physical sunscreen and chemical sunscreen. They have different ingredients and different protection principles. Physical sunscreen reflects or absorbs ultraviolet rays, while chemical sunscreen reacts chemically with ultraviolet rays and absorbs them, thereby protecting the skin from less damage and achieving a sunscreen effect. As ordinary consumers, we need to pay more attention to these two parameters of sunscreen.

There are two common parameters for sunscreens: SPF (sun protector factor), which indicates the ability to resist UVB and prevent skin from getting sunburned or sunburned. SPF is an international standard, and the sun protection factor = 1/(1-UV filtration rate). The larger the index, the stronger the protection ability, but the upper limit is 50. The duration of sunscreen (min) can be calculated based on the index * 10, of course, the premise is that it must be fully applied.

PA (Protection Grade of UVA) indicates the ability to protect against UVA, that is, the ability to prevent sunburn. The protection ability is represented by a "+" symbol, and the more the better the protection effect . There are also PPD and other symbols for UVA protection ability, and different countries adopt different standards.

Image source: pixabay

It is recommended to refer to the above indicators and then choose a suitable sunscreen based on your own outdoor conditions.

As for which is better, "blocking sunscreen" or "applying sunscreen", if it is in the scorching summer, it is best to use both methods together. That is to say, apply a layer of sunscreen while physically blocking, adding an extra layer of "barrier" for the skin, which can achieve the best sun protection effect.

3

Avoid These Sunscreen Mistakes

Many people insist on sun protection every day, but still get tanned. In fact, it is because they do not do effective sun protection, which leads to half the result with twice the effort. Some people do not like the "greasy feeling" brought by sunscreen on their skin, and prefer to use an umbrella or wear long sleeves. However, when it comes to sun protection, there is also a "knowledge" in using an umbrella and wearing clothes.

To effectively protect yourself from the sun, you should choose a parasol that has low light transmission and a black rubber layer, and a sun-protective clothing that has a tight structure and is dark in color . If you don't want to use an umbrella, you can choose a hat, and try to choose a hat with a wide brim that can cover your face. Of course, in the summer or at noon when the sun is strong, it is best to "take a two-pronged approach" and apply an extra layer of sunscreen.

Sunscreen contains a lot of oil-soluble additives to dissolve the sunscreen ingredients. If you don't apply enough to keep your face dry, it will not protect you from the sun . And sunscreen has a time limit. Many people apply sunscreen before going out, but as mentioned earlier, long-wave ultraviolet light UVA can penetrate glass, which means that you will be exposed to the sun when working by the window or driving. Once the time limit has passed, even indoors, the skin is still exposed to ultraviolet radiation, so it is recommended to reapply sunscreen at least every three to four hours. Friends who have cars can also apply film on the windshield.

Secondly, the sun protection index is generally recommended to be greater than 30, and the PA index is above +++ . There are also requirements for the amount of sunscreen applied. The standard dose is two milligrams per square centimeter. It is usually recommended to use a one-yuan coin-sized amount on the face, and apply it to other parts of the body in a similar proportion.

Image source: pixabay

Sunscreen does not take effect immediately after being applied. It needs to form a film on the face before it can work. Therefore, it is recommended to apply it ten minutes in advance before going out. Sunscreen needs to be applied after moisturizing products to prevent the formed film from being destroyed .

Regarding sunscreen sprays, most of them are water-based and have a thinner texture. They are lighter, drier and more refreshing than sunscreen creams, but they are also easy to evaporate and need to be reapplied multiple times. They are more suitable for use on a large area of ​​body skin. If used on the face, they can easily spray into the eyes, mouth and nose.

In general, sun protection is not just about whitening, but more importantly, it is about protecting the skin. Whether you are a man or a woman, young or old, you need to pay attention to the health of your skin. With the arrival of hot summer, hurry up and prepare sunscreen products!