Red bumps on the arms in summer may be diseases such as insect bite dermatitis and polymorphic sun rash, which can be treated with topical as well as oral medications. 1. polymorphic solar rash: is an idiopathic, recurrent, polymorphic lesions characterized by a common light-sensitive skin disease, preferably in the forearms and other exposure areas, aggravated in spring and summer. You can use topical glucocorticoid drugs, such as halometasone ointment, mometasone furoate cream, etc., combined with oral antihistamines, such as loratadine, cetirizine and so on. Going out to do a good job of sun protection measures. 2. insect bite dermatitis: summer mosquitoes are more, easy to bite the skin exposed areas caused by insect bite dermatitis, can be used externally with glucocorticoid drugs, such as dinexed cream, etc., if the itching is serious, you can take oral antihistamines, such as chlortetracycline for anti-allergy treatment. If red bumps on the arm in summer, pay attention not to scratch, avoid exposure to the sun, it is recommended to go to the hospital to find a doctor to deal with, follow the doctor’s instructions to use medication, do not blindly use drugs.