A moisturizer is the first thing a person buys when thinking about skincare. Do you know that the concept of "moisturizing" does not exist at all? Let's figure out where the water comes from in the skin, and where it goes.
Water in the skin performs the same functions as in any other part of the body: it participates in chemical reactions, is a service for the delivery of nutrients to cells and promotes the removal of harmful substances, helps the body adjust to the ambient temperature. And also promotes proper healing after any damage.
If we are talking about the aesthetic component, then water is responsible for the density and elasticity of the skin. Its deficiency provokes a dull complexion, flabbiness, tightness, wrinkles, and inflammation (due to a lack of moisture, more sebum is produced).
The main thing to understand is that the main path of water in the skin is from the inside out, and not vice versa. In the inner layer (dermis), water enters through the blood vessels. Further from the dermis, it penetrates the outer layer (epidermis).
It is more difficult to introduce water through the skin than through the vessels: the skin has an epidermal barrier, and this is a reliable barrier. Until recently, it was believed that the penetration of water from the surface of the epidermis into the skin was impossible: the H20 molecules are too large. But recent research has shown that the epidermis is linked to the dermis by a chain of nanochannels called aquaporins. They are nano-sized protein structures that open on the surface of the skin and a certain number of water molecules do penetrate the dermal layer.
In 2003, Peter Agre received the Nobel Prize in Chemistry for his discovery of aquaporins. Interestingly, this study was not originally related to human skin but examined organisms of mammals and plants.
Does the water in the skin exist in the form of drops? Or in the form of molecules? Or maybe somehow else? Basically, water molecules are bound. That is, they are hydrogen-bonded with proteins or other molecules. But about 20% of water is free molecules. No one has yet succeeded in calculating the exact ratio due to the difficulty of measurements.
Most (up to 80% of the total) is contained in the deep layers of the skin, where there are living cells. In the upper, stratum corneum, consisting of dead scales, there is much less water (from 15% to 30%).
Today physiologists distinguish three main water pools that exist in the skin - static, dynamic, and transdermal. They communicate with each other, and a deeper pool can supply water to more superficial ones, but water from the "upper" pools cannot return to deep ones.
The static pool is the volume of water that is constantly present in the epidermis. In healthy young people, its amount can be up to 30% of the total volume of the epidermis. Hyaluronic acid and natural moisturizing factor (NMF) retain water between the cells of the stratum corneum, binding water molecules with amino acids, lactic acid, urea. If this pool is full, the skin is smooth, even, and there are no fine wrinkles.
The dynamic pool is located deeper - this water reserve is located at the dermis level. In the dermal layer, water is retained by a matrix consisting of glycosaminoglycans, the most important of which is hyaluronic acid. The dynamic pool is responsible for the firmness, density, and elasticity of the skin.
Even lower is the transdermal pool - water contained in the microcirculatory chain of the skin (dermis capillaries).
Reaching the upper cells of the epidermis, water evaporates. This is called transepidermal water loss. It also comes out with sweat and flows through the lymphatic vessels. External influences - high and low temperatures, chemical or physical (UV radiation) factors - damage the protective layer of the skin and increase water loss.
In the dermal layer, hyaluronic acid is responsible for water retention. A decrease in its amount leads to a decrease in moisture level, which happens with age. There is also a hyaluronic between the living cells of the epidermis but in a much smaller amount.
It is worth starting with the fact that in medicine there is no concept of "moisturizing" at all. This word was invented by marketers. Typically, manufacturers use this term for three categories of products:
1. Emollient (lipophilic) - fill the gaps between the scales in the stratum corneum and make the skin smooth to the touch. Softening: lipids, oils, fatty alcohols, and fatty acids (stearic, linoleic, oleic, and lauric).
2. Moisturizer - create a film and prevent transdermal water loss. Create occlusion: mineral oil and its derivatives, lanolin.
3. Hydrophilic moisturizers (Humectant or Hydrator) - getting into the epidermis, they attract moisture from the dermis and the environment. Attract moisture: glycerin (it has no equal), hyaluronic acid, lactic acid, beta-glucan, propylene glycol, butylene glycol, panthenol, urea, sorbitol, AHA acids.
Right. As we wrote above, the main path of water in the skin is from the bottom up, and not vice versa.
In order for all layers of the skin to be saturated with water, you need:
1. Maintain moisture in the transdermal pool of water, that is, the water that is contained in the capillaries of the dermis, namely:
2. "Moisturize" the stratum corneum with the ingredients mentioned above. Despite the fact that it consists of keratinized cells, water is needed for their adhesion. If there is not enough water, water will be drawn out of the dermis.
3. Maintain a healthy lipid barrier. In addition to lipids and fatty acids, this is facilitated by antioxidants: ferulic, ascorbic acids, vitamin E, resveratrol. They protect their lipids by preventing them from oxidizing in the sun.
4. Stimulate the synthesis of aquaporins, which facilitate the transport of water from the top to the bottom. Their number decreases with excessive solar radiation, the use of certain acids, and simply with age. Stimulation of the synthesis of aquaporins is a promising and insufficiently studied branch in dermatology. These ingredients are supposedly considered to be plant extracts of pomegranate, algae, and apple.
5. Do not be nervous. Under stress, the hormone cortisol is produced, which decreases the production of its own hyaluronic acid.
There are practically no medical indications for moisturizing the skin. Exceptions are the rarest manifestations of extreme dryness of the skin, in which cracks occur. But the level of hydration certainly affects the visual appearance of the skin. A hypothetical healthy person with a healthy body and, accordingly, healthy skin, living in a hypothetical ideal climate and not facing aggressive environmental factors can do without additional moisture.
A real person in the modern world still needs additional moisture. At the very least, because his skin is exposed to the sun and hard water every day. And then there is a so-so ecological situation, stress, unhealthy diet. All this negatively affects the moisture level.
During some periods, such as on vacation in humid climates, normal skin will actually feel great without the added hydration. But this is rather an exception. For the average person, a combination of two to three moisturizing products works best without too many problems. For example, a moisturizing toner and/or moisturizing serum with antioxidants and a "covering" cream that prevents moisture evaporation and restores the lipid barrier.
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