The red rash on the inner thigh root may be caused by contact dermatitis, ringworm and eczema. 1. Contact dermatitis: usually an allergic reaction or irritation reaction caused by friction of underwear or contact with allergens, the patient’s thigh root will have symptoms such as redness, itching and red rash. 2. Ringworm: ringworm is a large red rash on the inner thighs caused by fungal infection, which is contagious. After the disease may appear red spots, skin flaking, pimples and itching and other symptoms. 3. Skin eczema: most of the eczema lesions are dominated by erythema, papules and papules, and acute eczema will have obvious oozing tendency and be accompanied by itching of the skin. There are many causes of inner thigh rash, patients should go to the hospital in a timely manner, clear causes under the guidance of the doctor reasonable treatment.