A lot of red spots on the arm, consider is due to folliculitis, mosquito bites, contact dermatitis and other factors, you can choose general treatment, medication and other methods of relief. 1. Folliculitis: a lot of red spots on the arm, may be due to Staphylococcus aureus infection caused by folliculitis, accompanied by itchy symptoms, you can choose mupirocin, fusidic acid cream drug anti-infection treatment. 2. Mosquito bites: mosquitoes in the bite arm area, will inject trace toxins into the body, will make the patient appear local red spots and itching symptoms, you can choose to use topical glycerine lotion, zinc oxide ointment and other drugs, to achieve the purpose of cooling and itching. 3. Contact dermatitis: in contact with allergens or irritants will induce arm metamorphosis or irritation reaction, red spots on the arm accompanied by itching symptoms, can be used with the doctor external glycerite lotion, oral loratadine and other drugs anti-allergy treatment. A lot of red spots on the arm may also have other reasons, it is recommended to timely to the hospital, improve the examination, under the guidance of the doctor standardized treatment. The above drugs need to be used in accordance with medical advice.