The natural moisturizing system in human skin is composed of three substances: water, natural moisturizing factor (NMF) and lipids, which keeps the stratum corneum with a certain moisture content and maintains the skin's moisture and luster. Normal skin stratum corneum usually contains 10% to 30% water, when the skin is too dry, there will be rough surface, lamellar splitting, loss of elasticity, and even chapping.
The main factors that cause dry skin on a daily basis include cold climate, low relative humidity of the air and age. Entering the autumn and winter season, as the temperature drops, the human capillaries contract, the blood flow rate slows down, the operation and metabolism of the organs have slowed down, and the sweat glands and sebaceous glands in the skin have become "lazy", providing significantly less water and oil. When the moisture is reduced to less than 10%, the skin's tension and luster will disappear, and the skin will appear dry, rough, chapped and other manifestations, which will cause wrinkles. Therefore, it is very important to pay attention to moisturizing the skin.
* What Is a Moisturizer
The moisturizing function of cosmetics depends on the moisturizing agent in the formula.
Generally, the substance that can maintain and replenish the moisture in the skin cuticle, prevent skin dryness or make the skin that has been dry and has lost its elasticity become smooth, soft and elastic is called moisturizer. This kind of substance has the ability to bind water in the low humidity range, can replenish water to the skin, by controlling the exchange of water between the surrounding air, so that the skin water is maintained in a higher than normal water content of the balance state, thus alleviating the role of dry skin.
In addition, the addition of moisturizers to cosmetics will also play a moisturizing role in the cosmetics themselves, so that cosmetics can maintain a certain humidity during storage and use, helping to maintain the stability of the active ingredients.
* Classification of moisturizers
There are many types of moisturizers, and according to the chemical structure of the ingredients, common moisturizers can be divided into the following 6 categories:
Fatty Alcohols
Such as glycerin, sorbitol, mannitol, polyethylene glycol, xylitol, cetyl alcohol, lanol and so on. This kind of substance is easy to dissolve in water, skin feeling refreshing, mainly used in moisturizer cream, honey skin care products, toner and toothpaste and other products. Due to the specific odor of high fatty alcohols such as lanolin alcohol, the scope of their use is limited to some extent.
Fatty Acids And Their Salts
Such as sodium lactate, sodium pyrrolidone, sodium alginate, hyaluronic acid (also known as hyaluronic acid), especially hyaluronic acid, widely exist in the connective tissue of mammalian eyeball vitreous, cornea, joint fluid, its moisturizing ability is significantly better than the general moisturizer, often used in high-quality skin care products.
Fatty Acid Esters
Such as hexyl laurate, isopropyl myristate, isobutyl myristate, isopropyl palmitate, isobutyl palmitate, etc., this substance is a synthetic oil, can form a layer of fine, non-sticky protective film on the skin, is recognized as the best permeability of a class of moisturizers, and is conducive to improving the effect of other emollients.
Allantoin
Widely exist in nature, can be combined with a variety of substances to form double salt, not only can promote the skin, hair outermost water absorption capacity, and help improve the hydrophilic keratin molecules, widely used in cream, milk cosmetics and hair care products.
Ceramide
As a natural moisturizing factor, ceramide is a new generation of moisturizing agent developed in recent years, which is similar to the material structure of the skin stratum corneum, and can quickly penetrate into the skin and combine with the water in the stratum corneum in a network structure to play a moisturizing role.
Peptides
This type of substance is a compound of amino acids joined together by peptide bonds. Soluble natural peptide proteins are easily absorbed by the human body, providing essential nutrients for the normal metabolism of human skin and hair, thereby increasing the natural luster and elasticity of skin and hair, and are often used in creams, creams, lotions, skin care and hair care products. In recent years, peptide substances have gradually become a hot spot in the development of cosmetics formulations and new raw materials.
In addition, humectants can be divided into natural humectants and synthetic humectants according to the source. Among them, natural moisturizers are divided into human sources, plant sources, animal sources and aquatic biological sources, which have been favored by consumers in recent years. The natural moisturizer from the human body is mainly sweat and sebum, and the sweat discharged from the body surface has the effect of enhancing the hydration ability of the skin surface, which is also the main reason why the skin is easy to dry after frequent bathing in winter. Natural moisturizers of plant origin contain many natural vegetable oils, such as olive oil, coconut oil, nut oil, aloe vera, etc. The most common natural moisturizers of animal origin are mainly honey. Natural moisturizers derived from aquatic organisms refer to a variety of compounds extracted from Marine organisms, bacteria and fungi, such as polyketones, alkaloids, peptides, proteins, lipids, glycosides and isoamyl ketones, which are widely used in cosmetics for moisturizing and anti-aging.
In order to play a better moisturizing role, in addition to adding a certain amount of moisturizer in cosmetics, oil-soluble substances and water-soluble substances can also be created under the action of surfactants to create an O/W (oil-in-water) or W/O (oil-in-water) type emulsion system. O/W system water content is relatively high, low oil content, the use of skin feel more refreshing, can be used in lotion, facial cleanser and shower cream and other products, usually suitable for oily skin, or summer, night basic skin care. W/O system with high oil content and low water content, greasy skin feeling when applied, often used in sunscreen, isolation cream and foundation products, usually suitable for dry skin, or autumn and winter skin care moisturizing.
* Evaluation Of Moisturizing Effect Of Cosmetics
At present, the relevant supervision and regulations of cosmetics are gradually improved, and efficacy evaluation is a scientific way to verify the efficacy of cosmetics. The explanation and claim guidelines for moisturizing cosmetics are clearly defined in the "Classification Rules and Classification Catalogue of Cosmetics", that is, they are used to supplement or enhance the content of water, oil and other ingredients in the application site, and help maintain the moisture content of the application site or reduce water loss.
At present, there are two commonly used methods to evaluate the moisturizing effect: one is to evaluate and grade the skin condition by clinical visual and tactile evaluation; The second is through the instrument detection. Using common indicators of skin dryness as reference, including the determination of shedding index, the determination of moisture content in stratum corneum, and the determination of water loss through the skin, the difference of these indicators before and after the use of cosmetics was verified.
The exfoliation index is measured by using scotch tape to obtain the loose cells and scales on the surface of the stratum corneum, and using computer image analysis system to determine the area and thickness of the exfoliated part of the stratum corneum. The water content of the stratum corneum can be measured by nuclear magnetic resonance spectroscopy, attenuated total reflection-Fourier transform infrared spectroscopy or near-infrared spectroscopy. In vivo Raman confocal microscopy can accurately analyze the distribution of water in the stratum corneum at different depths. It is the most widely used method to measure the water content of the stratum corneum indirectly by measuring the capacitance, conductance and resistance of the skin. Most of the instruments present the results of measuring the water content of the stratum corneum in numerical form, and some instruments convert electrical signals into images, such as skin microscopes and active skin surface analysis systems. Moisture loss through the skin is also an important reference index to characterize the moisturizing effect of cosmetics. By measuring the skin moisture content and the transepidermal moisture loss value of different mass fractions of moisturizers, the moisturizing effect of cosmetics can be comprehensively evaluated.
In addition, the moisturizing effect of cosmetics can also be reflected by measuring the indicators related to skin water content, such as the determination of pH value. The pH of healthy skin is usually maintained at 4 to 6, and if the water content of the skin stratum corneum is reduced and the lipid on the skin surface is reduced, the pH value will be relatively increased.
In the dry season of autumn and winter, skin moisturizing can effectively ensure the skin soft and smooth and delay the formation of wrinkles, it is recommended that consumers can choose moisturizing products produced by different moisturizing agent formulations and preparation processes according to personal skin characteristics and different use scenarios. In addition, it is also necessary to pay attention to the appropriate amount of water supplement, fresh fruits and vegetables and other substances rich in vitamin E and vitamin C.
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