Mucus is made of proteins that bad-breath-bacteria find delicious!
When you have post-nasal drip, mucus drains down through your nasal passages and coats the back of your tongue and throat where bacteria live.This feeds the bad-breath-bacteria, which have a field day breaking down the proteins in your mucus into smelly and sour tasting compounds.
Providing a mucus food source for bad-breath-related bacteria can result in the rapid onset of bad breath. So, people who suffer with post nasal drip, sinus problems and other similar issues are more prone to bad breath and awful tastes. In fact, post-nasal drip happens to be one of the main causes of bad breath in children as they tend to get a lot of runny noses. Colds and sore throats can also feed bad-breath-related bacteria, which is why people with those illnesses can have a characteristic ‘sick’ breath odour.
Interestingly, the use of antihistamines for sinus problems can make a bad breath problem even worse. Antihistamines can dry the sinus area and slow the production of saliva. Less saliva means your body has less capacity to control bad-breath-related germs in your mouth which leads to even worse breath.