Common causes of brown spots on lips include anemia, smoking or drug use, dermatitis, sun exposure, certain medications and nutritional deficiencies due to eating disorders, according to Health Hype. Other possible causes of brown spots may be dry lips, jaundice or Peutz-Jeghers syndrome, which is associated with intestinal cancer.
Health Hype explains that the skin on most lips tends to be lighter than skin on other areas of the body or face because the lips have less melanin than skin in other areas. The lips also have fewer layers of skin. Genetics ultimately determine just how much melanin exists to color a person's lips, but lip color is also affected by exposure to ultraviolet light, blood flow and the color of tissues beneath the skin. This is the reason lips often have a pinkish or red tint. In most cases, when a person develops skin discoloration on the lips, it shows up as brown or grayish spots, but certain conditions may also cause lips to take on a yellow or bluish color, notes Health Hype. Anemia, one of the more common causes of brown spots on the lips, usually happens to women during their reproductive years. Anemia occurs when there is a low concentration of hemoglobin carrying oxygen through the blood. Anemia is often caused by an iron deficiency.