The beauty industry is under fire: Is skin hydration a "tax on intelligence"? Dermatologists respond like this...

Recently, a video went viral online. In the video, a woman asked experts in the skin care field when the "hydration lie" would end, and said that "the skin cannot and does not need to be hydrated." This question has attracted widespread attention. Today, let's talk about skin hydration and moisturizing from the perspective of a dermatologist.

Screenshot of the viral video. Swipe up and down to view

Does your skin need hydration?

Before discussing this issue, we need to first understand the structure of the skin.

The skin is composed of epidermis, dermis and subcutaneous tissue. The epidermis is the part that directly contacts the outside world. The stratum corneum, clear layer and granular layer in the epidermis are the key to retaining moisture.

Structure of the skin | Wikipedia

The stratum corneum generally contains 15% to 25% water. It not only prevents the dissipation of water in the body, but also absorbs water from the external environment.

When the water content of the skin is less than 10%, the skin will have difficulty in normal metabolism and its functions will be affected. The skin is like dry land, and the water, electrolytes and other substances in the skin are more likely to be lost through the skin. At this time, harmful substances from the outside world are also easy to invade, causing a variety of skin problems, such as skin itching, allergies, etc.

If the skin is well moisturized, the skin cells will be "saturated" with water, allowing the skin to form a "protective film" again, and the skin will regain its softness and smoothness. Therefore, the skin needs to be hydrated, especially dry skin or exposed to dry environments.

However, what we usually call "hydrating" is just hydrating the stratum corneum. Because of the protection of the skin barrier, moisture basically cannot reach the dermis. Skin care products that claim to be able to hydrate the dermis are all false propaganda.

Why sometimes more water

Dry skin?

We also need to clarify the relationship between hydration and moisturizing. Moisturizing is mainly to prevent the loss of water from the skin surface and form a moisturizing film on the outside to lock in moisture. This is also the medical term for reducing "transepidermal water loss". To give an example, the effect of moisturizing is similar to covering a layer of film on the land containing a certain amount of water to prevent the original water in the land from being lost too quickly. The real "hydration" is different. Hydration is similar to watering the land, and the purpose is to increase external moisture.

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Many people find that long-term use of moisturizing products does not improve dry skin, and even seems to make it worse. Why is this? Generally speaking, after cleaning the skin, the water content of the stratum corneum is about 30% before applying skin care products. Using skin care products can increase the water content of the stratum corneum to 70%~80% in a short period of time.

If you only use moisturizing products, such as moisturizing spray, the moisture on the skin surface will evaporate into the air, causing the skin to become drier. So if you want to "quench the thirst" of your skin in an air-conditioned room and just moisturize, your efforts are in the wrong direction. Using moisturizing cream while moisturizing can better lock in moisture in the skin and bring lasting moisturizing effects to the skin.

There are many hydrating and moisturizing products on the market

What are they?

There are many names for skin care water, including toner, astringent water, softener, functional water, essence water, etc. They mainly have two common functions.

One is to moisturize. Using skin care products after washing your face can temporarily increase the water content of the skin. After applying moisturizing cream, the water will be locked in the skin, achieving a long-lasting moisturizing effect, which may be better than using moisturizing cream alone. Of course, if you don't use this kind of skin care water, it is not impossible to just use moisturizing cream to moisturize.

The other is secondary cleansing, which helps remove residual cleanser and makeup while adjusting the skin's pH level.

In addition, the water quality in some areas is hard, and washing your face with hard water for a long time will cause damage to your skin. Because the pH value of skin care water is precisely adjusted, it can neutralize the acid-base imbalance of the skin caused by various reasons when used on the skin surface, so that the skin can reach the best state. Skin care products with different names have different effects. You need to carefully distinguish them when purchasing and choose the one that suits you best.

1. Toner

It has strong cleaning and pH adjustment functions, and is more suitable for people who often wear makeup. It is best to dip it with a cotton pad and apply it in one direction on the face. It is best not to apply it directly with your hands, because your hands may not be clean enough, and the dirt cleaned will still remain on your hands or face, which will not achieve the purpose of cleaning.

2. Astringent water

It contains ingredients that help shrink pores and control oil, and is more suitable for oily skin. It should be noted that this type of lotion may contain alcohol, so people with sensitive skin and allergies need to be careful.

3. Toner

It is mainly used for moisturizing and softening cuticles, and has a weak cleansing effect. You can apply it directly on your face with your hands. Some products with moisturizing ingredients have a thicker texture, between water and dew, and will have some additional effects when used before moisturizing cream.

4. Lotion

Lotions and creams have a strong water-locking function, and some also contain ingredients that repair the skin barrier. They are the most mainstream and recommended moisturizing agents. Among them, the biggest feature of lotions is their high water content, which can instantly moisturize the skin and build a layer of moist sebum film for the skin to prevent moisture loss. Compared with creams, lotions have a more refreshing texture and are more suitable for summer or neutral, combination and oily skin types.

5. Facial Cream

Facial cream is essentially the same as lotion, and the change in the shape of the cream is just a process issue. In addition to the basic function of moisturizing, some also contain other functional ingredients, such as repair and anti-wrinkle. Night cream is usually more nourishing than day cream, and will feel greasy after use. It is more suitable for use in dry autumn and winter or dry and neutral skin.

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How to choose moisturizing products?

A good moisturizer is a must-have for every beauty lover. There are many types of moisturizers on the market, and the main active ingredients are divided into three types: occlusive agents, hygroscopic agents and emollients.

Occlusive agents can form an oil film on the surface of the skin to prevent water from evaporating, such as petrolatum. Humophores are substances that can absorb water. They can attract water from deep in the skin to the stratum corneum, or absorb water from the environment with high water content. Emollients are a class of mild, lipophilic substances that can make the skin softer and tougher. Different moisturizers are different ratios of these three types of substances.

So how do you judge whether a moisturizer is good or not? There is a simple method that can be used as a reference. A famous domestic skin expert once said, "You only need to try this product on your face or body, and the feeling of your skin is the best answer." A good moisturizer can provide a long-lasting moisturizing feeling, and the skin will be moist, smooth and elastic after use.

Of course, when choosing any skin care products, you must remember to purchase products produced by regular manufacturers that meet national standards.

References

[1] Zhu Xuejun, Wu Yan. Learn skin care from skin experts. Beijing. People's Medical Publishing House, 2016. [2] Hao Fei. Expert consensus on the application guidance of moisturizing and emollient products (2023 edition) [J]. Chinese Journal of Dermatology, 2023, 56(8): 711-717. doi:10.35541/cjd.20230133.

This article is a work of Science Popularization China-Starry Sky Project

Produced by: Science Popularization Department of China Association for Science and Technology

Producer｜China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

Author: Feng Jun, deputy chief physician of the Dermatology Department, General Hospital of Datong Coal Mine Group Co., Ltd.

Reviewer: Tang Qin, Director and Researcher of the Science Popularization Department of the Chinese Medical Association

｜Tang Jiaoqing, attending physician of dermatology, doctor of medicine