Waking up in the morning with a black tongue may be caused by food debris. If it still exists after carefully brushing your teeth and rinsing your mouth before going to bed, it may be related to an infection of the body or a gastrointestinal dysfunction. 1. Body infectious diseases such as pneumonia cholecystitis exists, causing the body’s immune system is in a state of stress, bacteria and viruses multiply on the tongue, there will be a black tongue. 2. Gastrointestinal dysfunction is due to disease or psychological factors caused by gastrointestinal abnormalities, in addition to black tongue, accompanied by acid reflux, nausea, vomiting, etc., a large number of flora breeding on the tongue, the appearance of black tongue, bacterial infections caused by black tongue can be treated with antibiotics, and viral infections can be used to alleviate the symptoms of anti-viral oral solution. So, waking up in the morning with black tongue is mostly seen in bacterial or viral infections, but also may be related to gastrointestinal tract dysfunction, if you can’t get rid of it by brushing your teeth and gargling, it is recommended to go to the stomatology department or gastroenterology department for medical treatment.