Acne is a very common chronic inflammatory or non-inflammatory clinical condition of the skin, usually located in areas with a high density of follicular sebaceous glands, such as the face, chest and neck, and back. Typical acne manifestations include non-inflammatory lesions, such as blackheads, and inflammatory lesions, such as abscesses, papules, or nodules with topical medication. Topical medications are the primary treatment option for mild to moderate acne, with salicylic acid, benzoyl peroxide, and vitamin A for non-inflammatory acne, and additional antibiotics or other antibacterial measures for inflammatory acne. Topical treatments have fewer side effects, mostly symptoms of skin irritation, and in general, gels, lotions, and solvents are more likely to cause dry skin than creams and ointments. Topical retinoids Clinically common retinoid formulations include retinoic acid (1st generation), tazarotene (3rd generation), and adapalene (3rd generation). Common adverse reactions include epidermal peeling, erythema, dryness, burning sensation, or pruritus, and are dose-related in severity. Among them, tazarotene is the most irritating, with local skin irritation occurring in about half of the patients who use it daily; adapalene has fewer adverse reactions and is well tolerated by patients. In addition to this, topical application of retinoic acid increases skin sensitivity to UV rays and therefore requires the combination of sunscreen or shades, etc., in daily life. Retinoic acid-mediated skin irritation tends to be self-limiting, usually peaking in the fourth week after administration, and then gradually improving. When benzoyl peroxide and salicylic acid are used in combination, retinoic acid-mediated adverse reactions such as epidermal peeling and erythema are exacerbated. Retinoic acid-mediated systemic adverse reactions are currently rare. Retinoic acid and adapalene are pregnancy category C drugs and are contraindicated in pregnant women, while tazarotene is pregnancy category X. Recent studies have found that topical retinoic acid during early pregnancy does not increase the risk of spontaneous abortion or fetal birth defects. Topical antibiotics Commonly used topical antibiotics include clindamycin and erythromycin. Common skin irritations include erythema, dryness and burning pain. Other topical medications Benzoyl peroxide is a class of non-antibiotic antibacterial medication that inhibits the growth and reproduction of bacteria such as Propionibacterium acnes through the production of reactive oxygen species. Isotretinoin is a metabolite of vitamin A. It is usually used to treat severe inflammatory acne, nodular cystic acne, or intractable disease.