The cause for the pigmentation needs to be determined. Smoking is one of the common causes for darkened lips. Stop smoking if you smoke. The darkness can also be present because of nutritional causes OR because of inflammatory conditions(like seborrheic or perioral dermatitis) OR with a superadded component of perleche. A proper detail examination would be required to try to assess and identify the culprit cause. Also you can use Chaptex lip balm twice a day for a few months. Hope this was helpful.

First stop smoking, use sunscreens, for 3minths