Isotretinoin is an effective drug against acne. It takes effect on four processes of acne procedures, preventing the formation of acne lesions: inhibiting sebaceous secretion; inhibit the growth of acne bacillus; inhibiting sebaceous hyperplasia; anti-inflammatory effect. Isotretinoin has no affinity to Vitamin A acid receptors. Its exact mechanism of action is not very clear. Its anti-acne role may be related to that it or its metabolites can inhibit the proliferation and differentiation of sebaceous glands. It may also reduce the volume of the sebaceous glands, reducing the skin's DHT, down-regulate the expression of skin androgen receptor. Other possible mechanism includes reducing the hair follicle keratosis, antibacterial, anti-inflammatory effects and so on. In the 1980s, Isotretinoin is only for treating severe nodular cystic acne. Isotretinoin is now also used for treating some less-seriously acne where those related patients are often insensitive to conventional therapy, especially some patients with long-term use of antibiotics due to that acne bacillus have evolved multiple drug (such as erythromycin, tetracycline) resistance. It may also be used for some acne patients prone to scar.