The hard packs on the back may be epidermal cysts or acne, which need to be analyzed specifically. 1. Epidermoid cysts: hard bags on the back are likely to be the manifestation of epidermoid cysts, which are a kind of dermal cysts containing keratin, due to inflammation, the back skin is not well cleaned, trauma and other reasons lead to the onset of the disease, the patient usually do not have self-conscious symptoms, and if there is a subsequent secondary infection there may be pain. 2. Acne: When excessive oil secretion or sebaceous gland keratinization abnormalities can lead to oil can not be discharged normally, bacterial infection of the follicular opening caused by local chronic inflammatory disease, thus leading to the symptoms of acne, the serious stage can form nodules, cysts. At the same time, we also need to consider the possibility of fibroma, folliculitis and other diseases, it is recommended that patients with serious symptoms of hard packs on the back, or the symptoms continue to not get better, should be timely to the hospital, after a clear cause to give targeted treatment.