Mild acne presents with predominantly acne with a small number of papules and pustules and less than 30 total lesions. Moderate acne presents as acne with a moderate number of papules and pustules, between 30 and 100 pimples, and nodules. Severe acne presents as nodular, cystic acne or aggregated acne with pain and cyst formation, with more than 100 pimples and more than 30 nodules and cysts. Photodynamic therapy uses LED red light irradiation for acne treatment after topical application of skin photosensitizers. After effective irradiation by laser light of specific wavelengths, photochemical reactions are generated with the participation of oxygen in tissues, producing monomorphic oxygen and free radicals, which destroy biological macromolecules in tissues and cells, eventually causing necrosis and apoptosis of target tissue cells to achieve treatment purposes, while having basically no effect on normal cells. It can directly kill Propionibacterium acnes and selectively destroy part of the sebaceous glands to reduce hair follicle obstruction. It is highly effective in treating papules, pustules and cystic nodules, and is the leading technology and preferred method for acne treatment at home and abroad. It also stimulates the growth of skin collagen, thus promoting the recovery of damaged areas. The laser not only effectively cures acne, but also simultaneously repairs acne pits, marks and scars left behind by acne, restoring the skin’s healthy natural luster.