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The most important “feel” of skin aging is dryness, which is manifested by low moisture content and lack of ability to retain moisture. The skin becomes crunchy, rough and flakes. A highly hygroscopic substance for the purpose of replenishing skin moisture and preventing dryness is called a humectant. The skin moisturizing mechanism, one is moisture absorption; the other is the barrier layer (defense layer) that prevents internal moisture from dissipating. The moisture penetration of this barrier layer when its function is normal is 2.9g/( m2 h-1)±1.9g/( m2 h-1), and when it is completely lost, it is 229g/( m2 h-1)±81g/( m2 h-1), indicating that the barrier layer is very important.

According to the moisturizing mechanism, a variety of moisturizers with good effects have been developed. Commonly used humectants include polyols, amides, lactic acid and sodium lactate, sodium pyrrolidone carboxylate, glucolipid, collagen, chitin derivatives and so on.

(1) Polyols
Glycerin is a slightly sweet viscous liquid, miscible in water, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-amyl alcohol, ethylene glycol, propylene glycol and Phenol and other substances. Glycerin is an indispensable moisturizing raw material for O/W-type emulsification system in cosmetics. It is also an important raw material for lotion. It can also be used as a moisturizer for powder-containing pastes, which has a soft and lubricating effect on the skin. In addition, glycerin is also widely used in toothpaste powder products and hydrophilic ointments, and is also an important part of hydrogel products.
Propylene glycol is a colorless, transparent, slightly viscous, hygroscopic liquid. It is miscible in water, acetone, ethyl acetate and chloroform, and dissolved in alcohol and ether. Propylene glycol is widely used in cosmetics. It can be used as a wetting agent and moisturizer for various emulsified products and liquid products. It can be used as a softener and moisturizer for toothpaste when compounded with glycerol and sorbitol. It can be used as a moisture regulator in hair dye products.
1,3-Butanediol is a colorless and odorless viscous liquid with good moisture retention ,it can absorb water equivalent to 12.5% (R.H.50%) or 38.5% (R.H.80%) of its own mass., less irritating than glycerin and propylene glycol. It can be widely used as a moisturizer in lotions, creams, lotions and toothpastes. In addition, 1,3-butanediol has an antibacterial effect. Sorbitol is a white crystalline powder made from glucose as a raw material. It has a slightly sweet taste. Sorbitol is easily soluble in water, slightly soluble in ethanol, acetic acid, phenol and acetamide, but insoluble in other organic solvents. Sorbitol has good hygroscopicity, safety, and good chemical stability. It has been widely used in the field of daily chemicals. It can be used as a raw material for non-ionic surfactants and can also be used as a cream in toothpaste and cosmetics.
Polyethylene glycol is a water-soluble polymer prepared by the gradual addition of ethylene oxide and water or ethylene glycol. It can also be dissolved in most strong polar organic solvents and has a series of low to medium molecular weights. The product type can be used as a water-soluble colloidal ingredient in various cosmetics. Polyethylene glycol is widely used in the cosmetics and pharmaceutical industries because of its excellent properties such as water solubility, physiological inertness, mildness, lubricity, skin moisturization, and softness. Low molecular weight polyethylene glycol has the ability to absorb and store water from the atmosphere, and it is plasticized and can be used as a humectant; as the relative molecular weight increases, its hygroscopicity drops sharply. High molecular weight polyethylene glycol can be widely used in daily chemical, pharmaceutical, textile, papermaking and other industries as a lubricant or softener.

(2) Lactic acid and sodium lactate
Lactic acid is an organic acid that exists widely in nature. It is the final product in the metabolism of anaerobic organisms. It is safe and non-toxic. Lactic acid is also the main water-soluble acid in the natural moisturizing factor (NMF) of the human epidermis, and its content is about 12%. Lactic acid and lactate affect the tissue structure of protein-containing substances, and have obvious plasticizing and softening effects on proteins. Therefore, lactic acid and sodium lactate can make the skin soft, swell and increase elasticity. It is a good acidifier in skin care cosmetics. The carboxyl group of lactic acid molecule has a good affinity for hair and skin. Sodium lactate is a very effective moisturizer, and its moisturizing ability is stronger than traditional moisturizers such as glycerin. Lactic acid and sodium lactate form a buffer solution that can adjust the pH of the skin. In cosmetics, lactic acid and sodium lactate are mainly used as conditioners and skin or hair softeners, acidifiers to adjust pH, creams and lotions for skin care, shampoos and conditioners for hair care and other hair care products. It can also be used in shaving products and detergents.

(3) Sodium pyrrolidone carboxylate
Sodium pyrrolidone carboxylate (PCA-Na for short) is a decomposition product of fibroin aggregates in the epidermal granular layer. The content of the skin’s natural moisturizing factor is about 12%. Its physiological function is to make the skin’s stratum corneum soft. The reduced content of sodium pyrrolidone carboxylate in the stratum corneum can make the skin rough and dry. Commercial sodium pyrrolidone carboxylate is a colorless, odorless, slightly alkaline transparent aqueous solution, and its hygroscopicity is much higher than that of glycerin, propylene glycol, and sorbitol. When the relative humidity is 65%, the hygroscopicity is as high as 56% after 20 days, and the hygroscopicity can reach 60% after 30 days; and under the same circumstances, the hygroscopicity of glycerin, propylene glycol, and sorbitol is 40% after 30 days. , 30%, 10%. Sodium pyrrolidone carboxylate is mainly used as a humectant and conditioner, used in lotions, shrink lotions, creams, lotions, and also used in toothpaste and shampoos

(4) Hyaluronic acid
And hyaluronic acid is a white amorphous solid extracted from animal tissues. It is a disaccharide repeating unit of (1→3)-2-acetylamino-2deoxy-D(1→4)-OB3-D glucuronic acid The composed polymer has a relative molecular mass of 200,000 to 1 million. Hyaluronic acid is a natural biochemical moisturizer with strong moisturizing properties, safe and non-toxic, without any irritation to human skin. Hyaluronic acid is soluble in water but insoluble in organic solvents. Due to the stretching and swelling of the molecular structure in its aqueous solution system, it still has a high viscosity at low concentrations, and can bind a larger amount of water, so it has excellent moisturizing properties, high viscoelasticity and high permeability.
Hyaluronic acid is currently a kind of moisturizer with excellent performance in cosmetics. In cosmetics, it can provide moisturizing effect on the skin, make the skin elastic and smooth, and delay skin aging. Many of the company’s hydrogel products contain hyaluronic acid or are used in combination with it, and have achieved good response after being introduced to the market.

(5) Hydrolyzed collagen
Collagen is also called glial protein. It is a white fibrous protein that constitutes animal skin, cartilage, tendons, bones, blood vessels, cornea and other connective tissues. It generally accounts for more than 30% of the total protein content of animals. It is in the dry matter of skin and dermal tissue. Collagen accounts for as much as 90%.
Collagen is the basic protein component that constitutes animal skin and muscle. It has good affinity with skin and hair. Skin and hair have good absorption for it, allowing it to penetrate into the interior of hair, etc., showing good Affinity and efficacy. And after hydrolysis, the polypeptide chain of collagen contains hydrophilic groups such as amino, carboxyl and hydroxyl, which can show good moisture retention to the skin. Hydrolyzed collagen also has the effects of reducing skin spots and eliminating wrinkles induced by ultraviolet rays. Therefore, the role of hydrolyzed collagen is mainly reflected in moisturizing, affinity, freckle whitening, anti-aging and so on. In animal tissues, collagen is a substance that is insoluble in water, but it has a strong ability to bind water. The hydrolysis of collagen can be carried out through the action of acid, alkali or enzyme, and soluble hydrolyzed collagen can be obtained, which is widely used in cosmetics and medical beauty products.

Other types of humectants include chitin and its derivatives, glucose ester humectants, and plant humectants such as aloe and algae.

Post time: Nov-17-2021