Many brown spots on the arms may usually be caused by a variety of reasons, such as hyperpigmentation, sun spots, coffee spots, lichen planus, seborrheic keratosis, etc. Patients are advised to visit the dermatology department of the hospital to help clarify the diagnosis, and the causes are usually seen in the following areas: 1. Pigmentation: mainly due to local inflammation, trauma, allergic rash and some diseases such as liver cirrhosis, resulting in local skin color deepening or an increase in the amount of pigment, often appearing as brown, tan or black spots on the skin. It can be treated by using depigmentation agents, retinoic acid drugs and physical therapy such as laser; 2.Sun spots: also called solar dermatitis, after strong sun exposure, within a few hours or the next day, the sunburned skin becomes red and swollen, accompanied by burning sensation and stinging pain. It is not affected by sunlight and can occur in any skin area. It exists in some normal people at birth and gradually appears during the growth of some patients. Generally, no treatment is needed, and those who have the need for beauty can choose the appropriate method to get rid of it; 4.Plaque fungus: it is a fungal infection disease, mainly manifested as abnormal pigmentation spots or patches with clear borders, and sometimes can be fused into patches, generally no other conscious symptoms, some patients can appear brown or black spots on their arms; 5.Seborrheic keratosis: mainly manifested as one or several yellowish or light brown, slightly higher than The reason for this is age, genetics, sun exposure, drugs, viral infections and air pollution, etc.; 6, flat warts: human papillomavirus infection caused by the face, back of the hand and forearm, the main performance of the number of flat papules, the color can be normal skin, gray or brown, the surface