You’re driving home from a first date, and it went great: You didn’t sweat too much, your jokes worked 50 percent of the time, and she didn’t get an “emergency phone call” in the middle of dinner. Only one thing stands in the way of your impending make-out session: the garlic bread you just ate. What’s your move? Gum. But can you be sure it will work? Science says yes, as long as the garlic is the worst of your problems.

Bad breath originates from three different sources: the nose, the stomach and the mouth. While more serious problems like acid reflux and sinus infections may underlie the smell, the most common source of halitosis is the mouth. “Everyone has bacteria in their mouth,” says Dr. Christine Wu, Professor and Director of Caries Research at the University of Illinois at Chicago’s College of Dentistry. “There are billions of bacteria in one little chunk of plaque.”

There are billions of bacteria in one little chunk of plaque.
Normally, the good bacteria balance the bad to form a healthy, odor-free ecosystem in your mouth. Your baby breath turns rancid when anaerobes overrun the system. These bacteria, which flourish in the absence of oxygen, usually live at the back of the tongue, where they are partially protected from oxygen and spit by a film of food, dead cells and mucus. Another source of stench is plaque, which your dentist has probably been lecturing you about since grade school. Eating too many sweets and failing to brush can cause plaque buildup on your teeth, which may spread into the pockets of your gums. Here the bacteria in plaque can cause not only gum disease, but terrible breath.

If you don’t brush your teeth and the bumpy area on the back of your tongue every day, these bacteria will thrive and give you bad breath. Alternatively, if you are sick and your immune system can’t maintain the balance of good and bad, anaerobes will reproduce very quickly, spreading through your whole mouth. This is the white coating you sometimes see on your tongue when you’re sick: smelly bacteria.

What makes bacteria particularly offensive (and not so different from humans in this way) is their excrement. Dentists call this waste “volatile sulfur compounds,” or VSC, and it has a foul odor, explains Dr. Cassiano Kuchenbecker Rösing, associate Professor of the Department of Conservative Dentistry at the University of Rio Grande do Sol in Brazil. The smell is comparable to rotten eggs, and is the difference between bad breath and get-away-from-me breath.

Extra spit works like a power washer, rinsing bacteria away.The good news is that there is a second line of defense against these harbingers of evil: enjoying a stick of gum. Gums with strong scents can cover unwanted odor, but they can also actively fight the odor-causing bacteria with a twofold attack. “The stimulation of saliva, which happens with chewing gum, is responsible for diminishing the bad breath,” says Rösing, whose research finds that gum can temporarily reduce VSC production by more than 70 percent. The extra spit works like a power washer, rinsing bacteria and VSC away.

Ingredients can also make a difference. Wu’s lab studies essential oils, which have the surprising ability to freshen breath. “Chewing gum can be a delivery system for [these] agents to kill germs,” she says. To date they have found a number of effective ingredients, including cinnamon, peppermint and spearmint oils, as well as green and black teas. Wu says some plant oils act on the bacterial membrane, making it leaky and killing the bacteria. Teas, on the other hand, kill bacteria by attacking their metabolisms and affecting their growth.

The trick is to find gums with real essential oils, a task harder than you may think. Labels commonly list the umbrella term ‘natural and artificial flavors,’ wherein the natural flavors may or may not be essential oils. Wu’s tested recommendation: the “kiss a little longer” gum itself, Big Red.

This story was produced in partnership with Northwestern University’s Medill School of Journalism. For more FYIs, go here.