Pimples turning into hard bumps may be caused by nodular acne, secondary infections, sebaceous cysts and so on. 1. Nodular acne: Nodular acne is caused by abnormal keratinization around the hair follicles of acne, or increased levels of androgens and an overly humid environment, and is manifested by acne lesions that become hard. 2. Secondary infection: If the acne is irritated by squeezing or not paying attention to the cleanliness of the acne area, secondary purulent bacterial infection may cause acne to become hard. 3. Sebaceous cysts: Sebaceous cysts may form locally due to recurrent or chronic acne. Due to the blockage of sebaceous gland ducts, sebaceous gland excretion obstacles, and gradually stagnate into hard pimples. In normal life, we should pay attention to local hygiene, avoid scratching. It is recommended to go to the regular hospital in time, under the guidance of professional doctors to clarify the diagnosis, targeted treatment.