Brown spots on the arm may be related to hyperpigmentation and lichen planus, which can usually be treated by physical therapy and medication. 1. Hyperpigmentation: If patients do not take good sun protection measures for their arms during outdoor activities, resulting in long time exposure to ultraviolet rays, it will be easy to cause hyperpigmentation, which will lead to the situation of brown spots on arms. For this situation, patients can usually apply physical therapy to deal with it, such as laser spot removal. 2. lichen planus: lichen planus is a fungal infectious disease, which is mainly manifested as spots or patches with abnormal pigmentation, and the color can be brown or reddish in addition to white, and there are generally no other conscious symptoms. There can also be brown spots on the arms. Usually, it can be treated with topical antifungal drugs, such as terbinafine hydrochloride cream, butenafine hydrochloride cream and so on. There are other reasons for brown spots on the arm, and it is recommended that patients go to regular hospitals in time to find out the cause of the disease and then carry out standardized treatment, so as not to delay the condition.