Red rashes on the roots of thighs may be caused by eczema, ringworm and other factors. 1. Eczema: Eczema is an allergic skin disease, such as localized excessive sweating, underwear material is too rough, repeated friction stimulation, may lead to localized eczema-like changes. Mainly manifested as local itching, papules, papules, scratching vesicles have obvious oozing. 2. Ringworm: ringworm is caused by dermatophyte infection, can occur in any part of the body, can also occur in the groin, resulting in localized ring-shaped or half-moon shaped red rash, gradually spreading to the surrounding area, usually accompanied by obvious itching. The red rash at the base of the thighs, it is recommended to go to the dermatology department of the hospital in a timely manner, to clarify the cause of the disease, and then follow the doctor’s instructions for treatment.