Unsatisfactory forehead contours such as local depression or excessive protrusion can also be fine-tuned by injecting collagen to create a smooth and full forehead. Collagen has a long history of clinical use, and its main products are from animals. After removing the sensitized amino acid series, the remaining substances are similar to collagen in the human body, which can be injected into the human body and eventually absorbed by the human body. When the forehead is full, collagen is directly injected into the deep soft tissue of the forehead with a syringe to make the forehead full.