The arm grew a lot of brown spots, may be caused by solar dermatitis, general treatment can be; if it is a florid chaffing rash, you can use ketoconazole cream, miconazole cream, etc.; if it is caused by flat warts, can be used locally external salicylic acid for treatment. 1. solar dermatitis: if the patient is in a long time after the sun, the arm grew a lot of brown spots, consider solar dermatitis, the patient should be detached from the sunburn environment, go out and do a good job of sunscreen, to avoid recurrence of the disease, appropriate supplementation of the loss of water electrolytes. Blisters pay attention to lesion care, do not scratch, so as not to aggravate the condition. 2. maculopapular furfura: patients with a lot of brown spots on the arm, and the rash gradually increased to the size of the nail cap, clear boundaries, the surface is covered with chaffy scales, usually considered as maculopapular furfura. You can use external ketoconazole cream, miconazole cream and other drugs, or oral itraconazole, fluconazole, ketoconazole and other drugs for treatment. 3. flat warts: brown spots on the arm, slightly elevated flat papules, considered flat warts, can be used topically salicylic acid, 0.05% ~ 0.1% retinoic acid cream and other drugs for treatment, but also for laser treatment. The above medications are to be used in accordance with the doctor’s instructions. There may be other reasons why there are a lot of small brown spots on the arm, patients should seek timely medical treatment, standardized treatment or treatment, do not blindly deal with their own.