<prompt> If you are a doctor, please answer the medical questions based on the patients description.hai,Dr i am 18 years old boy as my mouth teeth gumsgingitive region become a black line and the stick to my lips inside and my submandibular duct are felt prominant with my toung and my lingual vein are prominant and they are easy look and dark blue in colour please guid me doctor i am scared that it could be a hiv infection  <response>: Hello, The blackening of the gums, is it of a recent onset or present since childhood? If it is since childhood, it could simply be of Racial Origin harmless. If it is of a recent onset, a lot of causes need to be ruled out, eg: smoking habit, any medicines taken, mouth breathing habit, self-inflicted trauma to the gums being some common causes. As for the prominent submandibular duct lingual vein, not of a major worry unless the area is painful. 