What causes black spots on human lips?

Environmental, behavioral and medical factors can cause black spots on the lips. Potential causes may include excessive consumption of hot coffees and teas, lip biting, a vitamin B deficiency or hormone imbalances, according to HealthGuidance.org.

In some cases, behaviors such as constant lip licking, smoking, drinking and the application of old and expired lipsticks may cause dark spots on the lips, notes HealthGuidance.org. Medical conditions such as large amounts of iron in the body and allergic reactions to medications or toothpastes may cause dark spots to appear on the lips. Hyper-pigmentation is another possible cause. In rare cases, dark or black spots on the lips may be a sign of skin cancer.