Darkened, chapped lips can lead to a bad first impression. They make you look unclean and unhealthy. Causes of black, chapped lips range from the body's absorption of toxic ingredients to the lack of proper lip care. Hyperpigmentation sun's rays harm all parts of the body, including the lips. The lips are especially vulnerable to hyperpigmentation, or an overproduction of melanin. Overexposure to ultraviolet rays causes hyperpigmentation. Applying lip balm with sunscreen in it prevents your lips from drying, cracking or changing colors. Wearing a scarf also stops the sun from damaging your lips..