Raised brown bumps on the skin may be caused by nevus pigmentosus, flat warts, seborrheic keratosis and other diseases. 1. Nevus pigmentosus: nevus pigmentosus is a benign proliferation of melanocytes, the etiology of which has not been clarified, and may be related to congenital heredity or developmental defects, triggers include ultraviolet light irradiation, medication, trauma and so on, the patient will be in the head, face, limbs and trunk and other parts of the skin lesions such as spots, pimples, plaques and so on, with a variety of colors, which can be brown. 2. flat warts: flat warts is a viral skin disease caused by HPV infection, the patient’s skin will appear slightly flat pimples, varying in size, the color is light brown or normal skin color. 3. Seborrheic keratosis: Seborrheic keratosis is a common benign tumor of the epidermis, most common in people over 40 years of age, the cause of the disease and skin aging, genetic susceptibility and other factors related to the patient’s head, face, neck, back of the hands and trunk and other places will appear brown spots, flat papules or plaques and other changes. There are more causes of raised brown bumps on the skin, and patients are advised to seek medical examination for a clear diagnosis.