Underarm ringworm-like erythema may be caused by ringworm, lichen planus, chronic eczema and other reasons. 1. ringworm: ringworm is caused by fungal infection, mainly in the human limbs and trunk, manifested as red papules or mounds on the surface of the skin, with the development of the formation of red patches, covered with scales, can be accompanied by varying degrees of itching. 2. Tinea versicolor: Tinea versicolor is a skin disease caused by Malassezia infection, which occurs on the chest, back of the shoulders, armpits and other parts of the sebaceous glands with strong secretion, and manifests itself as a pore-centered, bordered patchy rash on the surface of the skin, with the color of reddish or brownish, and the surface is covered with scales. 3. Chronic eczema: chronic eczema may be related to endocrine diseases, heredity, skin barrier damage, allergies, etc. It occurs in the hands and feet, armpits, calves and other parts of the body, and manifests itself as erythematous macules, papules and scales on the skin surface, accompanied by itchy symptoms of varying degrees. There may be other causes of ringworm-like erythema under the armpits, so it is recommended to go to the hospital in time, improve the examination, and give targeted treatment under the guidance of the doctor after the cause of the disease has been clarified.