The redness of the arms in the sun may be related to physiological factors such as ultraviolet radiation, but also to diseases such as solar dermatitis and polymorphic sun rash, which can be remedied by general treatment and medication. 1. Physiological factors: If the arm is exposed to ultraviolet radiation for a long time, it may lead to localized redness. It is recommended to avoid further exposure of the arm to sunlight and keep the area clean and moisturized to help relieve the symptoms. 2. Solar dermatitis: sunburned arms may be related to solar dermatitis, the patient should drink more water, replenish body fluids, avoid sun exposure; can follow the doctor’s instructions for external use of glycerite lotion, can help to alleviate the local symptoms. You can also apply halometasone, hydrocortisone and other glucocorticoid ointment as prescribed by the doctor, which has anti-inflammatory properties and promotes recovery. 3. polymorphic sun rash: polymorphic sun rash may also lead to arm sun red, it is recommended that patients pay attention to local hygiene, pay attention to the sun, it is recommended that patients follow the doctor’s instructions orally hydroxychloroquine and other medications, with the regulation of immunity, anti-inflammatory effect, to promote recovery. There are many reasons for sunburned arms, after eliminating physiological factors, it is recommended that patients go to a regular hospital, under the guidance of the doctor, choose the appropriate treatment.