Hyaluronic acid, also known as hyaluronic acid, is one of the components of the human dermal tissue and is responsible for storing water and adding volume to the skin, making it look full, plump and elastic. As we age, hyaluronic acid continues to be lost and loses its ability to store water. Hyaluronic acid injection cosmetic treatment is to use the properties of hyaluronic acid to replenish synthetic hyaluronic acid into the body for filling and shaping cosmetic purposes. Generally speaking, the larger the molecular weight of hyaluronic acid for injection, the longer it exists in the body. Depending on the molecular weight of hyaluronic acid, it will generally be completely degraded within 6 months to 3 years after the procedure. In addition, depending on the molecular weight of hyaluronic acid, the duration of maintenance in the body varies. Hyaluronic acid with larger molecular weight is generally used for contouring plastic injection of nose, brow bone or chin; medium molecule can be used for filling forehead, apple muscle, temporal area, etc. The maintenance time is about 8-12 months, and the best shape can be maintained within half a year; while hyaluronic acid with smaller molecular weight is generally used for injecting forehead lines, or tear trough, which is generally absorbed within half a year, and the best shape can generally be maintained for about 3 months. However, these are not absolute, to maintain a more desirable effect, not that about six months absorption, the entire injection process repeated once in about six months. Candidates can make additional injections at the right time according to the absorption situation. In other words, the effect will be maintained for a longer period of time if the injections are supplemented by regular face-to-face consultations or according to daily self-observation, if there is a deficiency.