Do you still need sunscreen when the temperature drops? How to choose between physical sunscreen and chemical sunscreen?understand

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Entering September, the high temperature in most parts of our country has left the scene. The weather in early autumn is obviously not as hot as before. Do you still need sun protection when going out now? What is the difference between different sunscreens? What is the point of smearing? One article to understand.

1 Whether you need sun protection depends on the UV index

According to experts, it is mainly the ultraviolet band in the sun that causes damage to the skin. We can use the ultraviolet index in the weather forecast to understand the situation of ultraviolet radiation in the atmosphere. When the UV index reaches 5 or above, it is necessary to pay attention to sun protection.

　　2 Do I need to take sun protection measures on rainy days?

If it’s rainy and cloudy, is there UV radiation too? Do I also need to take sun protection measures?

In the laboratory of the School of Physics of Peking University, experts use the detector to collect the spectrum of sunlight in the outdoor cloudy environment, collect the data of ultraviolet rays in the sunlight on cloudy days, and then compare it with the spectrum of the same period of sunny days, and judge by data comparison Whether UV exposure has been reduced to the point where protection is not required due to cloudy weather.

Liu Kaihui, director of the Institute of Condensed Matter, School of Physics, Peking University: Our experiments show that the range of ultraviolet radiation on cloudy days is not too low, and it is still necessary to do ultraviolet protection.

Liu Aiying, a professor at the National Emergency Medical Research Center: Some people think that sunscreen is only needed on sunny days, and not on rainy days. This is wrong. Because ultraviolet rays still exist on cloudy and rainy days, just like UVA, it is an ultraviolet light with a particularly strong penetrating ability, so whether it is rainy or sunny, we also need to use sunscreen.

3 What is the difference between the different sunscreens? What’s the point of smearing?

For sun protection, many people apply sunscreen before going out. What is the point of applying sunscreen? How to choose?

According to different ingredients, sunscreens are mainly divided into physical sunscreens and chemical sunscreens.

Liu Aiying, a professor at the National Emergency Medical Research Center: After the physical sunscreen is applied to the skin, it prevents ultraviolet rays from reaching the skin and causing skin damage by blocking reflection and scattering. Chemical sunscreens are mainly some chemical substances. After being applied to the skin, they complex with the stratum corneum of our skin. Under the condition of ultraviolet radiation, a chemical reaction occurs to play the function of sun protection.

Physical sunscreens usually take effect immediately after application, while chemical sunscreens take a certain amount of time to form a protective film, and usually need to be applied 20-30 minutes before going out. So what is the correct way to apply it?

In the laboratory, the experts built a device to simulate the solar spectrum, and at the same time used a detector to simulate the sunlight that the skin feels, and the signal sensed by the detector will be displayed on the computer in the form of data for easy comparison .

Liu Kaihui, director of the Institute of Condensed Matter, School of Physics, Peking University: So the overall feeling is that the way of application may be very important. We can see that the application is relatively uniform and forms a dense protective film. If the protective product itself meets the standard, the protective effect will be very good. good.

Experts said that through experiments, it is easier to form a uniform protective layer by applying in circles, while spot coating and push-and-wipe coating tend to have different thicknesses of the coating. There will be good protection in thick parts, poor protection or even no protection in thin parts. The situation of the effect.

4 How to choose the right sunscreen?

In addition to physical sunscreens and chemical sunscreens, biological sunscreens have also attracted attention recently. What is the difference between them?

Biological sunscreens are based on physical sunscreens and chemical sunscreens with the addition of biological agents. According to experts, biological agents have a repairing effect to a certain extent.

Liu Aiying, a professor at the National Emergency Medical Research Center: Biological sunscreen is a protective repair function for skin inflammation caused by ultraviolet radiation, but it does not really prevent ultraviolet damage and skin irradiation, so in our daily life The most commonly used are physical sunscreens and chemical sunscreens.

Experts suggest that the use of sunscreen should be selected according to the different areas where you are, the length of outdoor exposure of the skin, and different skin types. People with skin diseases, sensitive skin, or people who have just undergone photoelectric therapy should try to use physical sunscreen Frost.

Liu Kaihui, director of the Institute of Condensed Matter, School of Physics, Peking University: We evenly smeared some products purchased randomly on the market on a transparent plastic sheet. We put this plastic sheet in front of the detector, and we will see the signal decrease on the screen. In fact, it simulates the decrease of ultraviolet light felt by our skin.

Three groups of physical sunscreens and chemical sunscreens were used in the experiment, and spectra were generated by collecting signals of simulated light passing through the sunscreens and shining on the detector, and compared them.

Liu Kaihui, director of the Institute of Condensed Matter, School of Physics, Peking University: From our test results, the effects of physical protection and chemical protection sunscreens are very similar in the short term.

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