Red bumps on the lower back, there are many diseases in dermatology that can manifest themselves as having an erythematous rash. The main diseases are the following: a. Allergic diseases, common eczema, papular urticaria, can be manifested as erythema, papular rash with varying degrees of itching, eczema rash types are diverse, can have scratches, crust, the course of the disease is slow, easy to recur, papular urticaria lesions are relatively single, mostly caused by mosquito bites, the course of the disease can be cured in about a week. The rash is characterized by band-like distribution of erythema, clustered set of divisional blisters, confined to one side of the torso with pinprick-like or burning-like pain, before the onset of the disease, most of the factors such as fatigue, colds, mental stress, etc., induced by a decline in immunity leading to viral infection. Third, erythematous scaling diseases, such as psoriasis vulgaris, can be manifested as erythematous plaques, it is recommended to go to the hospital for a face-to-face consultation to determine which disease to take the appropriate treatment.