Like other areas of the body, the mouth is full of germs. Those germs are mostly harmless. But the mouth is the entry to the digestive tract. That's the long tube of organs from the mouth to the anus that food travels through. The mouth also is the entry to the organs that allow breathing, called the respiratory tracts. So sometimes germs in the mouth can lead to disease throughout the body.
Most often the body's defenses and good oral care keep germs under control. Good oral care includes daily brushing and flossing. Without good oral hygiene, germs can reach levels that might lead to infections, such as tooth decay and gum disease.
Also, certain medicines can lower the flow of spit, called saliva. Those medicines include decongestants, antihistamines, painkillers, water pills and antidepressants. Saliva washes away food and keeps the acids germs make in the mouth in balance. This helps keep germs from spreading and causing disease.
Oral germs and oral swelling and irritation, called inflammation, are linked to a severe form of gum disease, called periodontitis. Studies suggest that these germs and inflammation might play a role in some diseases. And certain diseases, such as diabetes and HIV/AIDS, can lower the body's ability to fight infection. That can make oral health problems worse.