The red spots on the thighs may be caused by eczema, ringworm, keratosis pilaris or allergic purpura. 1. eczema: eczema is a relatively common inflammatory skin disease, usually and the environment, local stimulation or diet, etc., the main symptom is that the local red spots, pimples, part of the gradual fusion into a piece, the edge of the unclear, accompanied by symptoms of itching. 2. Ringworm: mostly occurs in the inner thighs, bilateral groin, manifested as a clear boundary of the erythema, the edge of the red papules can be seen, gradually expanding outward, itching obvious. 3. Keratosis pilaris: Keratosis pilaris, also called chicken skin, occurs on the outer thighs, usually associated with skin hyperkeratosis and thickening and blockage of keratin around the mouth of hair follicles. 4. Henochromatosis purpura: Henochromatosis purpura is also a relatively common skin disease, may be related to drugs and food, the main symptom is that the lower limbs of the shin before the skin will appear the size of the pinpoints of petechiae, petechiae, pressure does not fade, and individual is also accompanied by abdominal pain, as well as joint pain and other symptoms. Red spots on the thighs may also be caused by other reasons, the specific need to go to the regular hospital, a clear diagnosis, and then targeted treatment.