Humans share a common evolutionary heritage, which includes symbiotic relationships with bacteria. We have colonies of bacteria everywhere, and in most cases, they are beneficial to use, helping with digestion, mood, blood pressure and other varied functions.
In a healthy individual, bacteria flourish under the right conditions of temperature, oxygenation, humidity, acidity, and other internal environmental factors. In the healthy case beneficial bacteria outnumber the harmful ones.
When the environment changes, however, due for instance to reduced moisture, then harmful bacteria multiply and, in some cases, take over the niches occupied by the beneficial bacteria. Usually this is reversible when the individual hydrates appropriately. Sometimes the multiplying bacteria can cause temporary or sometimes irreversible damage like periodontal disease, or even fatal damage, for example, deadly infections that are non-responsive to antibiotics.
In the mouth, there are good and bad bacteria constantly present. For example, some good ones help with the production of nitric oxides lowering blood pressure, and some bad ones producing poor smelling substances like the rotten egg smell of hydrogen sulfide and methyl mercaptan.
When we wear facial masks that cover our noses and mouth, we are usually involved in some activities involving expenditure of energy. Which usually cause us to need hydration to replace the water used in cleaning our systems during any exertion. In addition, during this pandemic unusual environmental temperature have been at record highs.
Wearing a mask also involves restricting the intake of fluids since we are more reluctant to doff the mask, drink and replace the mask. We therefore tend to be more dehydrated during mask wearing. We are also not usually doing any oral hygiene practices such as brushing flossing or even lightly cleaning tooth surfaces with a toothpick to eliminate the burdens of bacteria.
When the oral system is dehydrated, the bacteria that produce sulfides and mercaptans are more favored in growth and as a result there is a higher quantity of these substances released than during more normal times, hence more bad breath.
Saliva is one of the bodies most potent inhibitors of bacterial growth. When you are dehydrated, this inhibition is diminished, and bacteria can grow rampant causing additional bad breath. The use of coffee, tea and alcohol increases dehydration due to their inhibition of Anti Diuretic Hormone (ADH). ADH increases fluid retention and the lack of it reduces the function of body fluids to produce saliva. As a result, when socializing with coffee or alcohol, there is a decrease in saliva and an increase in oral bacteria and bad breath.
Some helpful hints are to brush and floss, and to hydrate before donning a mask. Pay attention to satisfying thirst and maintain your normal oral hygiene practices to reduce the incidence and severity of bad breath.