Allergy test before use. The application is done by cleansing the skin and then applying salicylic acid to the skin to achieve complete removal of closed mouth acne by exfoliating the aged stratum corneum. There are some precautions to be taken when using salicylic acid. 1. It should not be used on sensitive and broken skin areas such as eyes and mouth. 2. Pay attention to the concentration of the salicylic acid product, you need to build up a tolerance level and start with a low concentration and low frequency. 3. Due to the presence of skin irritation, it is not recommended for people with sensitive skin or a thin cuticle. If burning sensation, redness or swelling occurs at the site of application, it should be rinsed with water and discontinued. If the situation is serious, you need to consult a doctor. 4. Pay attention to strengthening sun protection, to avoid the renewal of the stratum corneum by ultraviolet radiation stimulation, resulting in more serious hyperpigmentation. 5. Do a good job of hydrating and moisturizing after use, otherwise the skin will become dry and fragile. Salicylic acid has exfoliating and pore-reducing effects. It is a safer drug for removing closed mouth acne. It is recommended to use under the guidance of a doctor to avoid adverse reactions.