 It has been estimated that 90 million Americans or approximately 30% of the U.S. population currently suffers from bad breath on a regular basis. And for those of you who think, phew, I'm glad I'm not one of those, it is believed that people with bad breath can't actually smell the odor coming out of their own mouth. Maybe this is because they're used to it, or it's because when you sniff your breathing air from below, rather than in front where you're exhaling, either way, the mouth air of chronic malodour suffers, is tainted with compounds such as hydrogen sulfide, which produce a stream of foul air that can be gravely offensive to the people in their vicinity. The characteristic smells in halitosis include compounds that smell like feces, like scatol, the rotten egg gas hydrogen sulfide, a corpse-like aroma from cadaverine, a sweaty feet compound, putrescene for the smell of decaying meat, rotten cabbage, rotten fish, pee, apples don't sound so bad, and I don't even know what squashed bedbugs smell like. But the major compounds that contribute to oral malodour are the VSCs, the volatile sulfur compounds such as hydrogen sulfide. Bacteria in our mouth, predominantly on our tongue, have the capacity to produce these odorous sulfur compounds through putrefaction of sulfur-containing proteins. Okay, so what can we do about it? Many have concentrated on trying to reduce the bacterial load in the mouth with like antiseptic mouth washes, or finding ways to trap the VSCs. Mechanically, you can disrupt the biofilm of bacteria on the tongue, like with various tongue scraping techniques, though tongue cleaning seems to work more through reducing the substrates for putrefaction rather than the bacteria themselves. Okay, but if the substrates for VSC production are the sulfur-containing amino acids, and the sulfur-containing amino acids are derived mainly from animal protein, meat and dairy, what about using a dietary approach? The VSCs from animal protein may actually explain why carnivore poop smells so much different than herbivore poop. And indeed, eliminating the amount of consumed proteins may significantly reduce phetorex ore from the Latin-meaning stench mouth. The reason they add fats and alcohol is that they can both cause relaxation of the lower esophageal sphincter. Normally, the only time you exhale odors from your stomach is when you burp, because the sphincter at the top of the stomach prevents stuff from backing up, but alcohol or a fat-rich diet increases the relaxation of that sphincter, which further increases the risk and severity of bad breath. But most cases of halitosis occur due to the decay of food residues in the mouth by the bacteria that decompose proteins and amino acids and produces the volatile sulfur compounds. So the treatment of oral halitosis should involve not just professional advice on oral hygiene, but also diet. Dairy proteins, for example, are known to break down in the mouth, leading to the release of the amino acids that are rich in sulfur. Dairy products are rich sources of the milk protein casein, and casein is rich in the sulfur-containing amino acid cysteine, which is a precursor to the formation of the rotten egg gas hydrogen sulfide in the oral cavity. In fact, that's how you can test people for bad breath. Sistine Challenge Testing I just have people swish their mouth with it. When cysteine is degraded, not only do you get the hydrogen sulfide, which comprises a large part of the bad breath bouquet, but you get sulfhydral anions that fever the growth of the very bacteria within the mouth responsible for the protein putrefaction that's central to the production of oral malodour in the first place and to the development of gum disease. So it's not just a one-two punch, but a triple threat. Bad breath isn't just some aesthetic issue. These volatile sulfur compounds can be toxic to the gums, even at extremely low concentrations. Hydrogen sulfide reacts with collagen and can alter the protein structure, thereby rending your gums and jaw more susceptible to destruction. Then you can develop these pockets of putrid pus that can lead to more halitosis. The periodontal pockets are the second main source of the volatile sulfur compounds. Even people with mild periodontitis may have twice the risk of reporting bad breath. Finally, let me touch on the role diet has in so-called extraoral halitosis, bad breath that doesn't originate in the mouth. There are lots of drugs that can do it, including dietary supplements like fish oil, but there's another way people can smell fishy, trimethylamine. Trimethylamine urea is one of the largest causes for undiagnosed body odor. It's when you can't sufficiently metabolize a malodorous compound called trimethylamine, which is formed in your gut when you eat lots of choline. The textbook presentation is urine, breath, sweat, and reproductive fluid smelling, like rotten or decaying fish. But what many doctors don't realize is that the fish odor presentation may only occur in like 10% of individuals who have this predisposition. Yes, at high concentrations, trimethylamine has a foul, rotten fish odor, but at low concentrations it can just give you kind of an unpleasant, garbage-like breath. And because there are so many foods that are rich in choline, like the fact that there are eggs found in so many foods, you may not make the connection between your diet and your body odor. But you can always try cutting out foods like egg yolks for a few weeks and see if you smell any better.