Patients with a lot of red dots on the arm may be caused by atopic dermatitis, hemangioma, allergic purpura, etc. After clarifying the cause of the disease, patients can improve their condition through general treatment, medication, surgery and other ways. 1. Allergic dermatitis: patients with atopic dermatitis should pay attention to skin care and avoid contacting allergens such as pollen, dust mite, animal hair, etc. Patients can take antihistamine drugs such as cetirizine and ibastine as prescribed by the doctor, and also use topical medications, such as glycerol lotion, glucocorticosteroids and other treatments. 2. Hemangioma: patients should pay attention to rest, avoid overwork or emotional excitement. Patients can use topical β-blockers, such as propranolol ointment, timolol ointment, etc.; or glucocorticosteroids, such as dexamethasone ointment, etc., or oral propranolol, prednisone, sirolimus and other drugs for systemic treatment, or surgical treatment if necessary. 3. Anaphylactic purpura: patients can use antihistamines, such as promethazine hydrochloride, chlorpheniramine, etc.; drugs to improve vascular permeability, such as triclopyr, carbachol, etc.; glucocorticosteroids, such as prednisone, etc.; hemostatic drugs, such as carbachol, etc., for treatment under the guidance of a doctor. It is recommended that patients strictly follow the doctor’s instructions, do not change the dose of drugs or private abuse of drugs, so as not to affect the therapeutic effect, pay attention to the monitoring of the condition in life, once the condition worsens should be timely medical treatment.