Red raised plaques on the right upper arm may be due to urticaria, psoriasis, tinea corporis and other causes. 1. Urticaria: It is stimulated by various foods, drugs and other factors leading to the temporary expansion of small blood vessels in the skin mucosa and increased permeability, and local edema occurs. Patients’ skin lesions may be manifested as the appearance of lumpy elevated, bright red or pale white plaques of varying sizes. 2. Psoriasis: it may be caused by genetic factors, environmental factors, immune factors and other reasons. The initial lesions are red papules or macules, which gradually expand to become red raised plaques with clear boundaries. 3. Ringworm: It is mainly caused by fungal infections such as Trichophyton rubrum and Trichophyton mustelii. The first is a light red dot, gradually expanding outward and becoming round, oval or irregular. The skin and the edges of the damage are slightly raised and ringed, forming a red patch. It is recommended that patients with red raised plaques on the right upper arm go to the hospital in time and follow the doctor’s instructions for treatment to avoid delaying the condition.