Find an ointment the contains benzoyl peroxide, salicylic acid or alpha hydroxy acid. Many of these are available over the counter from brands such as Clearasil and Proactive. You may want to try a lotion that was scientifically developed for this purpose of eliminating buttocks breakouts, Butt Acne Clearing Lotion by Green Heart Labs.  Make sure to dry yourself off thoroughly and apply the ointment directly after showering. Let the ointment dry before putting clothes on, as benzoyl peroxide may bleach your clothes. You may alternatively use a product that contains Tretinoin, used to treat acne and wrinkles. Differin is an over-the-counter product that contains this retinoid.  Ask your doctor about which product is right for you. Some types of pimples may need antibiotic treatment in pill form. Ask your doctor about which antibiotic prescription is appropriate for your condition. If prescribed antibiotics, make sure to complete the pills for the number of days prescribed, even if your pimples clear up before the end of the cycle. Failure to do so may cause the pimples to return. If you have particularly large cystic pimples that are extremely painful, you can resort to a steroid injection. These can reduce the size and pain of a pimple in less than a day.

===
Write a summary of the previous text in Vietnamese:
Sử dụng thuốc bôi ngoài da hoặc kem dưỡng da sau khi tắm. Dùng thuốc kháng sinh. Tiêm steroid.