The important symptom of bad breath is a bad smell in the mouth, sometimes with gingivitis or indigestion. If bad breath is caused by poor oral hygiene, it is usually caused by the accumulation of food debris or soft scale around the gums, and there are symptoms of red and swollen gums or bleeding gums from brushing or eating, which are typical of gingivitis. Bad breath may also be caused by tooth decay resulting in nerve necrosis, bacterial infection with the distinctive odor of dead pulp teeth, and gum abscesses from apical infection, or tooth decay forming cavities, with food residue forming corrosive bad breath under bacterial fermentation, usually with symptoms of tooth pain or sensitivity. If the bad breath is caused by imperfect digestion in the gastrointestinal tract and the food is not completely decomposed in the stomach, there will be symptoms of indigestion, such as stomach pain or bloating and belching. In the case of bad breath of respiratory origin, most of it is caused by pneumonia or rhinitis, which may result in poor nasal ventilation, etc. So bad breath can sometimes coexist with symptoms such as bleeding gums, tooth pain, indigestion, and rhinitis.