Brown skin patches may be caused by coffee spots, sweat spots, seborrheic keratosis and other reasons. 1. Coffee spot: the specific pathogenesis of coffee spot is still unclear, belonging to a kind of hyperpigmented skin disease. It is a kind of hyperpigmented dermatosis, mostly occurring on the face and trunk, manifesting as brown patches of different sizes, shapes and boundaries on the skin surface. 2. Sweat patches: sweat patches are mainly caused by Malassezia infection, manifested as dotted patches on the skin surface. With the development of the disease gradually increase in size, the adjacent lesions will be fused with each other to form large irregular patches, the surface is covered with scales, and the color is brown, light brown, white, yellowish and so on. 3. Seborrheic keratosis: the pathogenesis of seborrheic keratosis is still unclear, and may be related to skin aging. Prevalent in adults over 40 years of age, manifested as patches, papules, plaques on the surface of the skin, the color can range from skin color, light black to brown. Brown patches of skin may also have other causes, it is recommended to go to the hospital in time for standardized diagnosis and treatment by a professional doctor.