Sinus Infection and Allergies
Some types of bacteria are strongly attracted to the proteins in mucus and phlegm. So, when a person has a sinus infection, head cold or allergies, the sinuses produce more mucous. Hence, when the extra mucus goes down the back of the throat, the breath will produce an awful smell. Generally, allergies are known to have the ability to produce cold-like symptoms like a sinus infection, sinus pressure, runny nose, and congestion. However, the condition is called allergic rhinitis, caused by an allergic response to allergens like pet dander, dust, and pollen.