Do this every day to slow down aging!

Author: Zhu Xuejun, Chief Physician, Peking University First Hospital

Former President of the Dermatology Branch of the Chinese Medical Doctor Association

Reviewer: Yang Dingquan, Chief Physician of China-Japan Friendship Hospital

Hair gradually turns white, wrinkles gradually increase, skin begins to become dry, and dark spots appear on the face... This physiological aging is a natural law that none of us can resist.

In addition to this physiological aging, there is another type of aging, called exogenous aging, which is mainly sunlight aging, or photochemical aging, which we can intervene artificially.

1. What is photochemical aging?

Compared with physiological aging, photochemical aging is more prominent. For example, people who are often exposed to the sun have rough skin, poor elasticity, and wrinkles all over their faces. We can see their aging very clearly.

In order to reduce this photochemical aging, it is particularly important to do a good job of sun protection in daily life. For example, applying sunscreen is mainly to block the medium-wave ultraviolet rays and long-wave ultraviolet rays from irradiating the skin.

The wavelength of medium-wave ultraviolet rays is 280-320nm. It mainly causes sunburn. For example, if you go to the mountains on a sunny day without applying sunscreen and stay in the sun for two hours, your skin will turn red at night, and after a few days, your skin will peel and turn dark. The sunburn we often talk about is mainly caused by medium-wave ultraviolet rays.

The wavelength of long-wave ultraviolet rays is 320-400nm. Long-wave ultraviolet rays are also called black light. They can slowly darken the skin, unlike medium-wave ultraviolet rays, which turn from red to black.

Generally speaking, medium-wave ultraviolet rays and long-wave ultraviolet rays are strongest between 10 am and 4 pm. During this period, we should pay special attention to sun protection. There are three main sun protection methods:

First, avoid sun protection, which means don’t go out when the sun is very strong and stay indoors.

Second, physical sun protection, including parasols, sun hats, sun sleeves, and wearing thicker, darker clothes, etc.

Third, chemical sunscreen, which is a variety of sunscreens. It absorbs light or reflects or refracts it, so that light only falls on the surface of the skin and does not penetrate into the inside. This is called chemical sunscreen.

Figure 1 Original copyright image, no permission to reprint

2. How to choose sunscreen?

There are various sunscreen products on the market, including emulsions, powders, wipes and sprays. You can choose according to your preferences.

In terms of properties, some are water-soluble and easy to clean; others are fat-soluble, which are difficult to wash off and need to be wiped with makeup remover first, and then cleaned with facial cleanser.

It is important to note that if you go to the beach or swim, you must choose fat-soluble sunscreen because ultraviolet rays can pass through water and there are also ultraviolet rays in water, so you also need sunscreen underwater.

In addition, you need to understand two indexes:

One is the anti-UVB index, also called the sunlight protection index, abbreviated as SPF in English. Now the SPF everyone uses is above 10, and the highest in our country is SPF50.

Generally speaking, using SPF10, 15, or 20 is enough. But if you are traveling and staying outdoors for a long time, you should use SPF30 or above. For example, if you go to the beach and swim, you should not only use waterproof makeup, but also SPF50.

In short, it depends on how intense the sun is and how exposed you are to the sun to decide what kind of sunscreen to use.

Another one is the long-wave ultraviolet protection index, abbreviated as PA in English.

PA is divided into +, ++, +++, ++++. In general living environment, PA++ is enough. However, if you go to Sanya, Southeast Asia, or travel to island countries, you usually need to use PA +++ or even PA++++.

Figure 2 Original copyright image, no permission to reprint

In addition, sunscreen products require 2 mg per square centimeter. Taking cream-based sunscreen as an example, the face will need about one and a half finger lengths of application.

What is the problem now? Many people don't apply enough, and the amount is too small; if it is summer, when you sweat a lot, you should reapply sunscreen every two to three hours, but some people don't pay attention to reapplying, so it can't really play a role in sun protection.

3. Is it okay to just use a parasol for sun protection without applying sunscreen?

Physical sunscreen has certain limitations.

Especially near the water, because the water surface is reflective, the ultraviolet rays blocked by the parasol come from above, and the ultraviolet rays reflected from the water surface must be blocked by sunscreen.

In addition to the water surface, ordinary ground, snow, including glass curtain walls, etc., will reflect ultraviolet rays, especially snow and glass, which reflect ultraviolet rays very strongly. So in addition to using a parasol, you should also pay attention to applying sunscreen.

Of course, if you rarely go outdoors and only go out to buy groceries occasionally, it is okay to rely on a parasol for sun protection for a short period of time, but for a long time, you still need to apply some sunscreen.