The symmetrical patches of yellow-brown patches on both sides of the inner thighs may be tinea cruris, eczema, post-inflammatory hyperpigmentation, and so on. 1. ringworm: ringworm is usually caused by dermatophyte infection, patients can be in the groin (unilateral or bilateral), perineum, perianal and other parts of the skin lesions such as pimples, blisters, scales, and there will be itchy symptoms, prolonged scratching leads to symmetrical yellowish-brown patches on the inner side of the thighs. 2. Eczema: it is an inflammatory skin disease caused by internal and external factors, often manifested as erythema, papules, accompanied by itching, etc., and in severe cases, erosion and oozing may occur, which may appear in the armpits, umbilical cord, groin and other parts of the body, and prolonged scratching may lead to symmetrical yellowish-brown patches appearing on the inner thighs. 3. Post-inflammatory hyperpigmentation: pigmentation abnormalities caused by various inflammatory dermatoses after cure can occur in all parts of the body. Therefore, yellow-brown patches on the inner thighs may also be caused by post-inflammatory hyperpigmentation. In addition to the above factors, the symmetrical patches of yellow-brown patches on both sides of the inner thighs can not be ruled out for other reasons, and it is recommended that the patient go to the regular hospital for examination in a timely manner, and after a clear diagnosis, carry out standardized treatment under the guidance of the doctor.