Answer: The answer to the question is Bacteria.
Bacteria colonization causes swelling and inflammation of mucous membranes.
Explanation: Bacteria colonization is the presence of bacteria in the body without causing any harm just like a normal Flora.
They become pathogenic and causing inflammation and swelling when the body's immune response is weakened or compromised by factors like autoimmune reactions,smoking,poor nutrition, alcohol and viral infections.
Bacteria colonization can occur in the skin,mouth,nose, gastrointestinal tract,urinary tract , respiratory tract and even the reproductive tract.