Small bumps on the buttocks after sitting for a long time are usually caused by acne, folliculitis, insect bite dermatitis, etc., and can be treated with medication and physical therapy under the guidance of a doctor. 1. Acne: Acne is generally caused by increased sebum secretion, follicular opening blockage and other reasons, there may be pimples, pimples, pustules and other symptoms, can be used under the guidance of the doctor Vitamin A acid, benzoyl peroxide gel and other medications, but also photodynamic, laser and other methods of physical therapy. 2. Folliculitis: folliculitis is usually caused by bacteria, fungi and other reasons, there may be local redness, swelling, pressure and pain and other symptoms, there may also be sitting for a long time on the buttocks long pimples, can be used under the guidance of the doctor fusidic acid cream, ketoconazole cream and other medications, but also to take the ultrashort wave, far infrared irradiation and other methods of physical therapy. 3. Insect bite dermatitis: pimples, skin swelling, itching and other symptoms will appear after the skin is bitten by mites and other insects, which can be treated with hydrocortisone, loratadine and other drugs under the guidance of doctors. It is recommended that patients go to the hospital and under the guidance of the doctor for reasonable treatment.