Hyaluronic acid originally exists in the skin, which can help the skin absorb the moisture on the body and skin surface, and also enhance the skin's long-term water retention ability. When hyaluronic acid absorbs water, elastic fibers and collagen are in a moist environment, so the skin is elastic. However, hyaluronic acid in the skin began to lose after the age of 25, leaving only 65% in infancy at the age of 30 and only 25% at the age of 60. The moisture of the skin will also lose its elasticity and luster with the loss of hyaluronic acid, and wrinkles will appear after a long time. Therefore, people over the age of 20 are suitable for using hyaluronic acid stock solution.