Erythema on the inner thighs may be caused by eczema, ringworm, dengue and so on. 1. eczema: eczema is a chronic inflammatory skin disease, may be the inner thigh skin moisture, sweat or underwear friction stimulation, usually manifested as red spots on the inner thigh, pimples, blisters, flaking and other symptoms, often accompanied by obvious itching. 2. Ringworm: ringworm is an infectious disease caused by dermatophytes, often appearing on the inner thighs, buttocks and other parts of the body, accompanied by erythema, blisters, scales and other symptoms, often accompanied by obvious itching. 3. Danovirus: Danovirus is an acute inflammation of the skin and subcutaneous reticular lymphatic vessels, Danovirus of the inner thighs is more common, the patient’s thigh skin will appear edematous erythema, and there will be pain, localized elevated temperature and other symptoms. If there is a situation of erythema on the inner thigh, it is recommended to go to the hospital in a timely manner, under the guidance of professional physicians, targeted treatment.