But what happens when the smelly shoe is on *your* foot? Everybody has bad breath from time to time -- and we're usually unaware when we do. What's worse, some estimates indicate that 40% of the population has *chronic* bad breath. It's virtually impossible to smell your own breath, and you're dependent on the kindness of loved ones to clue you in; friends, co-workers, and other casual acquaintances will be too "polite" to tell you. That's a problem. Multi-million dollar business deals have soured, love affairs ended, and once-in-a-lifetime opportunities vanished –- all because of bad breath. On the surface, it's not rational, but human beings are unconsciously affected by smells. It has something to do with the limbic system –- our ancient mammalian brain parts –- that links emotions to positive (and in this case) negative odors.

Sometimes you know the reason. Perhaps you've recently eaten a spicy, garlicky meal. (My wife and I have an agreement to both eat garlic at the same time, so we cancel each other out.) Very often, however, the cause is seemingly unknown. Understanding the "science" of bad breath will help you know when you're likely to have "silent" bad breath, and can take corrective action before major social damage occurs.

A primary source of breath odor are the volatile sulfur compounds given off by bacteria in your mouth. Of course, bacteria are always in our mouths. However these little guys vary greatly in their activity. Causes of increased volatile-sulfur compound activity include stress, gum disease, food debris, and dry mouth. Other factors associated with bad breath are diabetes, smoking, drinking alcohol in excess, mouth breathing, nasal conditions, allergies, and certain foods. The SEJU Engineering Kiss Me Meter works by actually measuring the level of these volatile sulfur compounds and hydrocarbon gasses in your mouth.

Know your alliums. Onions and garlic and other allium vegetables (leeks, chives, shallots, etc.) produce pungent amine compounds which enter our bloodstreams and are eliminated from the lungs during respiration, and often from the pores of the skin as well. However, there are many health benefits associated with eating these foods, and they taste great too. Fortunately, you have some control over your food choices, and can ask to "hold the onions" prior to an important social engagement.

Dry mouth is a very common cause of bad breath (particularly morning mouth). We need to produce copious amounts of saliva to wash away food bits and excess bacteria. When saliva production is reduced, because of dehydration, environmental conditions, some medications, or disease, the stagnant debris and bacteria causes a very unpleasant odor. Drinking lots of water is always a good idea, for a variety of health reasons, in addition to fighting bad breath. Daily flossing and thorough tooth brushing are essential to remove excess bacteria.

The back of your tongue is a hotbed of bacteria. Sorry. I know that's gross. However, you may want to consider brushing your tongue or using a tongue scraper/cleaner, particularly if you're getting negative feedback about your breath. You should know that breath mints, gum, mouthwash, and toothpaste can temporarily mask bad breath but will rarely cancel it out entirely. Severe cases of bad breath (halitosis) require treatment by a dentist or specialist.