It is currently believed that an ideal classification of acne severity should meet the following criteria: 1. be accurate and reproducible; 2. be simple and easy to use; 3. not require complex calculations or photography; and 4. be effective in guiding treatment. At present, a new classification method is mostly used internationally, namely the three-degree, four-grade classification method, which is based on the nature and severity of acne lesions. Grade 1 (mild): acne only; Grade 2 (moderate): inflammatory papules in addition to acne; Grade 3 (moderate): pustules in addition to acne and inflammatory papules; Grade 4 (severe): nodules, cysts or scarring in addition to acne, inflammatory papules, rashes and pustules.