Foul-smelling breath and fever may be caused by gastroesophageal reflux disease (GERD), Helicobacter pylori infection, etc. It may also be caused by diseases of the oral and periodontal systems, such as gingivitis or periodontitis. Gastroesophageal reflux disease (GERD) is a dysfunction of the lower esophageal sphincter, which causes the stomach contents (food or stomach acid) to flow back into the mouth through the esophagus, and the symptoms of foul-smelling breath and fever may occur; proton pump inhibitors (such as omeprazole, etc.) or H2-blocking agents (such as cimetidine, etc.) should be taken under the guidance of a doctor. Helicobacter pylori can parasitize in the gastric mucosa, locally decompose urea to produce ammonia, which damages the gastric mucosa and causes chronic gastritis as well as ulcer disease, which will lead to foul-smelling breath and fever; antibacterial drugs (e.g., penicillin, etc.) should be taken under the guidance of a doctor for treatment. Oral periodontal system diseases, such as: gingivitis or periodontitis, periodontal tissue inflammatory cell infiltration, plaque accumulation, caused by sulfide production, will make the mouth out of breath and smell and fever; should be under the guidance of the doctor for periodontal cleaning, care and so on. If the long-term mouth out of breath with odor and fever, should go to the hospital in time to find out the cause, symptomatic treatment, so as not to delay the condition.