Hyaluronic acid (HA) or uronic acid is a linear macromolecular polysaccharide composed of disaccharide units (glucuronic acid -N- ethylthioglucosamine), which is a naturally occurring substance in tissues. Widely distributed in connective tissue, mucous tissue, eyeball lens and some bacteria in nature, it plays an important role in the dermis of human skin, and plays an important role in the overall maintenance of tissue structure and the transportation between cells. ? Originally, hyaluronic acid was only used for moisturizing, but now it has been included in the ranks of wrinkle removal and plastic materials. This plastic surgery is based on non-animal stable hyaluronic acid fermented by bacteria, and hyaluronic acid is injected as a filler into the wrinkles and depressions of the dermis or the parts that want to be full, so as to achieve the effect of wrinkle removal and facial modification, which can immediately remove wrinkles and change appearance. Hyaluronic acid, which originally exists in the dermal tissue of human skin in the form of colloid, is responsible for storing water, increasing skin volume and making skin look full, plump and elastic. However, hyaluronic acid will disappear with age, making the skin lose its water storage capacity, gradually becoming dull, aging and forming fine wrinkles. Thanks to the progress of biotechnology, hyaluronic acid can be extracted from connective tissues of vertebrates, such as cockscomb, eyeball, umbilical cord and cartilage. In the past, hyaluronic acid was mostly extracted from animals, but now it is artificially synthesized, which avoids problems such as allergies and infections. ? With the development of science and technology, hyaluronic acid can not only be injected and filled, but also has been developed for external use. This kind of hyaluronic acid for external use contains hyaluronic acid, SOD, cell growth factor particles and other cosmetic components. Users are no longer just those who want to get rid of wrinkles and breast enhancement. Users of hyaluronic acid for external use can be beauty lovers with dark yellow skin, rough skin, dull skin, wrinkles and spots on their faces. Generally speaking, external hyaluronic acid is suitable for more people, although it has lost the traditional cosmetic effect of filling hyaluronic acid for breast enhancement.