Itching on both sides of the thighs can be caused by friction or sweating irritation, ringworm, or eczema, as follows: 1. Friction or sweating irritation: It is more commonly caused by friction, or sweating irritation, and may result in mild erythema or transient skin reddening. 2. Ringworm: If there are obvious well-defined erythema on both sides of the thighs, and the center of the erythema has a tendency to fade, most of them are ringworm. Tinea cruris is caused by dermatophytes invading the cortex of the femur, and patients also have significant itching discomfort.3. Eczema: Patients can have erythema at the root of the thighs, an allergic skin disease where the boundaries of the erythema are not clear and itching can be more pronounced.4. Other: Some rare causes, such as scabies, can also cause itching on both sides of the thighs.