2, for external use, because it can't penetrate the skin and be absorbed by the skin, it is only the moisturizing effect of the skin surface.
3. In addition to external use, it can also be injected into the superficial dermis through a water needle, or injected into the dermis with a syringe needle, which can play the role of moisturizing and local filling. Hyaluronic acid is widely used in dermatology and plastic surgery, but it will be metabolized over time after injection and needs to be supplemented.