Asthma is a condition of chronic inflammation of the lungs. Pneumonia is an infection of the lungs’ tissues, most commonly caused by viruses and bacteria. Both illnesses can present with similar symptoms, including cough, respiratory distress and hypoxia (low oxygen content in the blood).
Asthma does not cause pneumonia, but it can predispose a patient to pneumonia. This happens because asthma weakens the lungs’ ability to clear up mucous and other cellular debris, weakening the lung’s protective mechanisms against microbes.
Likewise, pneumonia can trigger an asthma attack. The body’s response to microbial infections in the lungs involves attracting white blood cells and releasing proteins involved in the generation of inflammation that kills the microbes. Some of these substances can also trigger the inflammation of asthma.