In humans, bad breath can originate from several different places in the body. Most people believe it only comes from the mouth, which indeed ranks as the most common source, but it may also flow from the tonsils, stomach and lungs.
For a handful of people, halitosis stems from the lungs. It might be connected with the two-way system in which we breathe, an idea inspired by a new study that explored the breathing patterns of lizards.
The study was led by researchers at the University of Utah and Harvard University, examining unidirectional breathing in savannah monitor lizards, which can be found throughout India, Africa, China and parts of southeast Asia. This system of inhaling and exhaling traces its roots back 270 million years ago in the ancestral group that gave rise to dinosaurs, and eventually alligators and birds.
Fascinatingly, one-way breathing was originally discovered in birds in the 1930s.
"It was first noted in birds that were living in train stations in Europe," Colleen Farmer, an associate professor of biology at the University of Utah and senior of author of the study, told LiveScience. "They were burning coal to power trains and noticed that only one part of the bird's lung was getting black with soot."
Unlike humans who breathe both out and in through the lungs in a "tidal," or two-way, pattern, the lungs in birds and lizards have same-direction airflow breathing. That means new air enters through a different gateway than where old air leaves.
To speculate, unidirectional breathing likely smells fresher than our two-way system. This is because when air flows in the same direction, more oxygen is transferred through the respiratory system with each breath. In other words, air in lizards and birds has a higher oxygen content than that of humans and other mammals, where new air is mixed with old air.
If you happen to own a pet lizard, you might want to take note. Otherwise, if you have a more conventional pet, say, a dog, keep an eye out for dog breath. Also, if someone says you have lizard breath, we guess they're paying you a compliment.