If the sputum in the mouth is more smelly, it means that there should be halitosis or other causes of foul odor in the sputum, there may be the following reasons: 1, orogenic halitosis, mainly due to gingivitis or periodontitis. In the presence of gingivitis or periodontitis, the dental neck hygiene is poor, often attached to a large amount of food debris, soft tartar, plaque, tartar. The bacteria on top of the plaque or tartar will use these food residues and soft tartar to decompose and produce some smelly gas, causing bad breath.2. Non-dental halitosis, for example, if it is a respiratory disease, there may be some bad odor in the sputum coughed up.3. There may also be a digestive system disease. If there is a disease of the digestive system, it can produce some foul gas in the stomach or intestines, and through the esophagus, pharynx or through the blood circulation, the foul smell will be transmitted to the mouth, causing bad breath.