There can be several causes why your skin would turn dark or you may get pigmentation. Sun tan, overweight, pigmentation disorders like acanthosis nigricans or melasma, nutritional deficiency etc are some conditions. Unless someone examines you, we cannot know the cause. Unless we find out the cause it is difficult and pointless to treat. Please send photos with detailed history using online consult option for examination and proper treatment.,

You are suffering from seborrheic dermatitis causing tan under mouth.. Medicine available for good improvement......As the treatment varies depending on the severity... Send photos of the affected area, by direct online consultation for accurate diagnosis and treatment.