Cysts are a type of lesion in severe acne. The clinical presentation is a soybean to fingertip-sized, oval-shaped, normal skin-colored or dark red cyst with a fluctuating sensation when pressed with the hand. The dermatopathological manifestation is a cyst without a cyst wall that is formed when the follicular sebaceous gland contains a large amount of keratinous material, a large amount of sebum and pus cells on top of a nodule, and intense inflammation occurs, destroying the entire structure of the follicular sebaceous gland and causing the accumulation of solid or liquid material. When the condition worsens, the cysts can become pus-filled and form abscesses. When adjacent abscesses converge, they form aggregated acne, which appears as large, irregularly shaped, round or globular lesions that break down and bleed a thick, viscous, yellowish fluid with blood. These cysts and abscesses leave atrophic or hyperplastic scars after healing, which seriously damage the beauty of the face and are also difficult to treat. Therefore, treatment for acne should be started early, and symptoms should be controlled at the early stages of the disease to try not to let the lesions develop into cysts. If deeper inflammatory damage such as nodules and cysts appear on the face, the first thing to consider is oral isotretinoin. It is able to target the four components of acne pathogenesis and is highly effective in treating all types of lesions. The commonly used dose is 0.5 to 1 mg/(kg.d) for 5 months, and the vast majority of patients can achieve prolonged remission. However, isotretinoin has a relatively high incidence of adverse effects, which can lead to teratogenesis especially in women of childbearing age. For this group of patients who cannot tolerate isotretinoin or for those who are slow to regress from damage treated with isotretinoin, other methods of treatment should be considered. The most commonly used topical treatment is the injection of corticosteroids into the lesions, which are particularly effective in reducing inflammatory papules, nodules and cysts, allowing them to dissipate rapidly. There are many options for corticosteroids, but the most commonly used clinically are tretinoin suspension and compound betamethasone injection (trade name Depo-Provera, manufactured by Schering-Polymer, USA) because of their strong anti-inflammatory effect and longer-lasting action, lasting more than 2 weeks. Trimethoprim is prepared in sterile saline to 5mg/ml or 2.5mg/ml, or even lower concentration, diluted to 1.5mg/ml (to try to avoid atrophy at the injection site), or the original solution of Depo-Provera or sterile saline dilution, for intracystic injection, and the dose given at the largest lesion should not exceed 0.1ml, and the total dose is usually controlled at 0.5ml to The total dose is usually limited to 0.5 ml to 1 ml. Cysts usually subside with one injection, and larger ones can be repeated with an interval of 3 weeks. Experience is very important when injecting corticosteroids within the skin lesion, and it is important to master the depth of the location and the time interval, otherwise it is easy to cause irreversible skin atrophy. For large cysts, local surgical treatment can also be used to make the lesions recede in larger pieces. The method is to first disinfect the lesion with iodine and alcohol, then take a small surgical blade and cut along the lower edge of the cyst along the skin line to expel the contents, so that no obvious scars will be left behind.