Bacterial respiratory infections are thought to be acquired through aspiration (inhaling) of fine droplets from the mouth and throat into the lungs. These droplets contain germs that can breed and multiply within the lungs to cause damage. Recent research suggests that bacteria found in the throat, as well as bacteria found in the mouth, can be drawn into the lower respiratory tract. This can cause infections or worsen existing lung conditions. People with respiratory diseases, such as chronic obstructive pulmonary disease, typically suffer from reduced protective systems, making it difficult to eliminate bacteria from the lungs.

Scientists have found that bacteria that grow in the oral cavity can be aspirated into the lung to cause respiratory diseases such as pneumonia, especially in people with periodontal disease. This discovery leads researchers to believe that these respiratory bacteria can travel from the oral cavity into the lungs to cause infection.

Chronic obstructive pulmonary diseases (COPD) cause persistent obstruction of the airways. The main cause of this disease is thought to be long-term smoking. Chemicals from smoke or air pollution irritate the airways to cause obstruction. Further damage to the tissue and working function of the lungs can be prevented, but already damaged tissue cannot be restored - untreated or undetected COPD can result in irreversible damage. Scientists believe that through the aspiration process, bacteria cam cause frequent bouts of infection in patients with COPD. Studies are now in progress to learn to what extent oral hygiene and periodontal disease may be associated with more frequents bouts of respiratory disease in COPD patients.