Convergence: Tannin and protein have condensation reactions by hydrophobic bonds and hydrogen bonds, which makes people feel convergence. The most direct effect of adding tannin to cosmetics is convergence. Cosmetics containing tannins have good adhesion to the skin under waterproof conditions, and can shrink and tighten the coarse pores to reduce wrinkles and make the skin show a delicate appearance. Tannin with sunscreen function is a kind of natural substance with strong absorption in ultraviolet light region. Tea polyphenols and persimmon tannins have been proved to be non-toxic to human body. The sunscreen cosmetics added with this kind of tannin are called "ultraviolet filters", which have an absorption rate of more than 98% for ultraviolet rays and have obvious resistance to solar dermatitis and various stains. Tannins and tannins, or tannins and flavonoids form molecular complexes by hydrophobic bonds and hydrogen bonds. On the one hand, they are complementary pigments, which produce * * * color effect and improve absorbance. On the other hand, it also improves the water solubility and makes them have synergistic effect. Whitening Tannin The color of skin is mainly determined by the content of melanin, which is synthesized by tyrosine in melanocytes catalyzed by tyrosinase under the action of ultraviolet rays. Tannin can not only absorb ultraviolet rays, but also inhibit the activities of tyrosinase and catalase, reduce and decolorize melanin, and effectively remove active oxygen, so adding tannin to cosmetics has a comprehensive whitening effect. Anti-wrinkle collagen forms a compact bundle in the dermis parallel to the skin surface. With the increase of age, the collagen in the skin is cross-linked under the action of active oxygen free radicals, which makes the structure firm, inelastic and wrinkles. Elastin is the most important fibrin to maintain skin elasticity. The decrease or denaturation of its content is the main reason for the decrease of skin elasticity and the formation of wrinkles. Inhibition of elastase's ability to degrade elastin is an important way to restore skin elasticity and delay wrinkles and aging. Tannin can scavenge free radicals and inhibit elastase activity. Some tannins can also promote cell metabolism and cultivate skin vitality to keep it healthy, shiny and elastic. Moisturizing effect Whether the skin looks healthy or not depends on the water content of the stratum corneum. Long-term lack of water will lead to rough skin and wrinkles. The molecular structure of tannin contains a large number of hydrophilic groups-phenolic hydroxyl groups. It is easy to absorb moisture in the air, so it has moisturizing effect. Hyaluronic acid is a mucopolysaccharide in the skin, which acts as a natural humectant. With the increase of age, hyaluronic acid will be decomposed by hyaluronidase, which will harden the skin and cause wrinkles. Tannin has a significant inhibitory effect on hyaluronidase, thus achieving a real physiological deep moisturizing effect. Anticorrosive effect Tannin has obvious inhibitory ability on a variety of bacteria, fungi and microorganisms, and will not affect the growth and development of human cells at the same inhibitory concentration. Tannin has unique oxidation resistance, which can effectively resist biological oxidation and scavenge active oxygen. Adding tannin to cosmetics can effectively inhibit bacteria and have health care and antiseptic effects.