Typically, Kawasaki disease and Peutz-Jeghers syndrome cause discolored lips, reports Merck Manual. Occasionally, people who smoke cigarettes develop noncancerous brown spots on their lips where the cigarette is usually held.
Peutz-Jeghers syndrome is a genetic disorder that is distinguished by the brown spots that appear on the lips, mouth and fingers, states MedicineNet. People with this condition have a higher risk for cancer. Kawasaki disease causes the lips to crack and the lining of the mouth to redden. It occurs in children 8 years old or younger. Freckles and melanotic macules are not a sign of illness but may last for years. As people age, their lips may become thinner.