HI. well i got ur problem but u must specify good history to find the cause for black patches. there are many causes like Excessive consumption of caffeinated/hot beverages such as coffee or tea lip licking or lip biting Large amounts of iron in the body.Vitamin B deficiency .Hormone Imbalances Allergic reactions to toothpastes/medication Smoking/Drinking can cause black marks Dry lips can sometimes develop into black spots or wounds Badly fitted dental fixtures Hyper-Pigmentation – Wherein there is too much pigment in the lips.Wearing old, expired lipsticks. u must visit the dermatologist to look for these causes by taking detail history from you. then he may be able to treat the condition. avoid hot foods and drinks.Another is to use chapstick, and to avoid licking or biting your lips. Avoid too much sun exposure which can dry them out and use moisturisers and drink lot of water to keep them hydrated.If you spend a lot of time outdoors exposed to the sun then make sure to wear a lipgloss or moisturiser with sun-block included. i hope u got my answer