A lot of red bumps on the back of the thighs may be related to folliculitis, eczema, contact dermatitis and other causes. 1. Folliculitis: when bacteria infect hair follicles, an inflammatory reaction can occur, manifested as single or multiple red bumps, which may be accompanied by pain. 2. Eczema: If you suffer from eczema, it is often caused by allergies and manifests itself as red bumps on top of erythema of the skin, often accompanied by itching. 3. Contact dermatitis: when the skin is in contact with allergens, it can cause localized red bumps, often accompanied by itching. There are a lot of red bumps on the back of the thighs, it is recommended to go to the regular hospital in a timely manner to clarify the cause of the disease, standardized treatment under the guidance of the doctor, so as to avoid delays in the condition of the body to bring about adverse effects.