Brown patches on your arms can be caused by sun spots, hyperpigmentation, age spots, flat warts, etc. 1. Sun spots. Prolonged sun exposure or strong sun exposure, the skin is sunburned, causing redness, swelling, tingling and other symptoms. Brown spots will appear after the redness subsides. 2. Hyperpigmentation. Patients previously suffered from eczema, pityriasis rosea, psoriasis and other diseases, after the rash subsides, it is easy to cause local inflammatory hyperpigmentation, which is manifested as brown spots. 3. Age spots. Mostly occurs in the elderly, there will be brown, flat and slightly protruding from the surface of the skin, the border is clear patches, may be accompanied by itching symptoms. 4. Flat warts. Caused by viral infections and other causes, they will appear as flat papules that may be brown, grayish-white, oval, round, or irregular. There are other causes of brown patches, you should go to the regular hospital in time, after a clear diagnosis of the symptomatic treatment, so as not to delay the condition of the adverse consequences.