Greetings. There can be few medical conditions associated with darkening of the lips and should be ruled out by meeting a Dermatologist. The information provided is limited. A thorough history and clinical examination will be helpful. A photograph will add in obtaining better recommendations.
Next Steps
You can meet a qualified Dermatologist with MD/DNB/DDVL/DVD degree for proper examination.
Health Tips
You can consult me online for personal recommendations.