The appearance of round red marks on the surface of the left foot of the elderly may be caused by ringworm, urticaria, pityriasis rosea, contact dermatitis and other diseases. 1. Tinea corporis: the disease is caused by dermatophytes, most commonly seen in Trichophyton rubrum, followed by Trichophyton broken hair, Trichophyton mustafasciatum, etc., which can be transmitted through direct contact or indirect contact. The main symptom is that the lesions have well-bordered red papules, blisters or plaques, so some patients will have round red marks on the surface of the left foot, which may be accompanied by itching and scaling. 2. Urticaria: The occurrence of this disease is related to heredity, infection, autoimmunity, mental nerves, contact with allergens and other reasons. Urticaria is mostly acute in onset, and the typical symptoms are the presence of itchy skin, round or irregular shaped wind bumps, etc. Therefore, the appearance of round red marks on the surface of the left foot of the elderly may be caused by urticaria. 3. pityriasis rosea: the etiology of this disease is not yet clear, after research performance, may be related to viral infection, drug exposure, immune dysfunction and other reasons. When the rash first appeared, the patient’s hands and feet, face, chest and other places will appear in rose-red, round or oval rash, which can be manifested as round red marks on the surface of the feet. 4. contact dermatitis; due to foot skin contact with certain allergens or irritants caused by the perverse reaction, there can be erythema, papules, itching, flaking and other manifestations, will also be manifested as the dorsum of the foot appeared round red marks. As there are more reasons for the appearance of round red marks on the surface of the left foot of the elderly, it is necessary to go to the hospital for consultation to clarify the cause of the disease.