I. Oral isotretinoin is the standard treatment for severe acne Oral isotretinoin is the standard treatment for severe acne, and is currently the most effective treatment for severe acne. Isotretinoin acts on all pathophysiological aspects of acne pathogenesis, and although the therapeutic effect is significant, it is not used as the first choice of treatment for mild acne as much as possible, considering its adverse effects. (2) Indications for the use of isotretinoin: (1) severe nodular cystic acne and its variants; (2) inflammatory acne with scar formation; (3) moderate to severe acne that has failed to respond to the following treatments: 3 months of combination therapy, including systemic tetracycline; (4) acne patients with severe psychological stress (disfigurement phobia); (5) gram-negative bacillary folliculitis; (6) frequent recurrences requiring repeated and (6) Patients with frequent relapses requiring repeated and long course systemic antibiotics; (7) A small number of patients who need rapid healing for some reason. Dose: The commonly used dose is 0.25-0.5 mg/(kg.d), and the dose should not exceed 0.5 mg/(kg.d) in order to reduce adverse reactions. The duration of treatment is determined by the patient’s body weight and the daily dose used. Third, the toxic side effects of isotretinoin Before the systematic use of retinoic acid, counseling and explanation to the patient is very important. It should be explained to the patient that retinoic acid can cause many adverse effects, especially teratogenic effects. Patients should use strict contraception for 1 month prior to treatment and until 3 months after the end of treatment. If pregnancy occurs during the course of treatment, abortion must be managed. A small number of patients develop depressive symptoms with the use of retinoic acid. Patients with a history of depression or in the family should use the drug with caution and discontinue it immediately in the event of mood swings or any depressive symptoms. Other adverse effects of isotretinoin are mainly dryness of the skin mucosa. There is a temporary exacerbation of acne in the initial phase. 5% of patients experience photosensitivity, joint and muscle pain, severe night blindness during night driving, severe hair loss, and blood triacylglycerols may be elevated. Liver function and lipid tests are performed prior to the start of treatment and are reviewed after 1 month of treatment. If both are normal, no further blood tests are required. Long-term high dose application may cause epiphyseal deformities such as osteophytes, calcification of the cremasteric ligament, and osteoporosis. It should be noted that isotretinoin should not be applied simultaneously with tetracyclines or systemically with glucocorticoids, because isotretinoin and glucocorticoids may synergistically induce an increase in intracranial pressure. Vivamate can also be used as an alternative to isotretinoin, but it is slightly less well absorbed orally, has a slower onset of action, and has relatively milder adverse effects.