Lips with dark edges, called hyper-pigmentation, is a feature of ethnicity. With this being said, it can make it difficult to treat patients with darker skin tones. This darkness typically gets more accentuated with sun exposure, so make sure that you are moderating any UV light exposure during the Summer.
Retin-A can help to lighten skin of any cause, especially when combined with hydroquinone and a very mild corticosteroid, like hydrocortisone, for a short period of time. In the botanical category, things like arbutin and licorice root have the most data on the holistic side for skin lightening.
