What causes bad breath or a bad taste in the mouth?

Bad breath (halitosis) may be caused by various factors. 1. Poor oral hygiene habits, such as infrequent tooth brushing, can lead to prolonged retention of food debris between teeth, resulting in odor production through bacterial fermentation. 2. Oral diseases such as gingivitis, periodontitis, and dental caries can also cause bad breath, as these conditions increase bacterial levels in the mouth. 3. Gastrointestinal disorders such as gastritis and gastric ulcers may lead to food retention and fermentation in the stomach, thereby causing oral odor. Additionally, certain systemic diseases such as diabetes and uremia can also contribute to halitosis. Therefore, improving bad breath requires comprehensive consideration of multiple factors including oral hygiene, dietary habits, oral health status, and overall health condition. If concerns persist, please consult a relevant healthcare professional.