Why Garlic Breath Outlasts Brushing, and What Lab Tests Found

Garlic breath can last for almost a day.¹ It also has a trick: brushing after lunch seems to work, and then the smell returns by midafternoon. Researchers have measured why.

The second wave

In 1999, five people ate 6 grams of garlic, and researchers measured sulfur gases in their mouth air, the air from deep in their lungs, and their urine.²

• Right after eating, most garlic gases were far stronger in the mouth than in the lungs, so they were coming from the mouth.²
• One gas, allyl methyl sulfide, showed up at similar levels in mouth air, lung air and urine. It had been absorbed from the gut, carried in the blood and breathed out.²
• By 3 hours, that gut-origin gas was the main sulfur gas on the breath.²

The authors’ summary: garlic breath starts in the mouth and later comes from the gut.² That’s why a toothbrush or mouthwash helps early and does little later. It was a five-person study, and it tested garlic only.

What lab tests found

Food scientists at Ohio State measured garlic gases on people’s breath with a lab instrument after they ate garlic and then something else.³¹

Tried after garlic	Result
Milk, whole or fat-free	Cut all the garlic gases measured; whole milk did better on the fat-loving ones3
Milk mixed into the garlic before eating	Worked better in the mouth than drinking milk afterward3
Raw apple, raw lettuce, mint leaves	Cut all the garlic gases measured1
Apple juice, mint juice	Helped, but generally less than the raw food1
Green tea	No effect1

Water did most of milk’s work, but milk beat water on allyl methyl sulfide, the persistent gas, in the mouth.³ The apple, lettuce and mint test tracked breath for up to an hour.¹ These were instrument readings, not ratings by people sitting across the table.

How to use this

• Eat the apple or salad with the garlic meal, or right after, while the smell is still mostly in the mouth.¹
• Drink milk with the meal if you like it.³
• Brush and clean your tongue for the mouth part. See how to use a tongue scraper.
• Plan for the afternoon. The later smell comes from your lungs, and no rinse reaches it.² See does mouthwash fix bad breath?

If your breath smells most days, no matter what you eat, see why your breath smells after brushing and how to tell if your breath smells.

Try: “My breath smells strong by afternoon even when I haven’t eaten garlic, and brushing doesn’t help. Could it be coming from somewhere other than my mouth?”

Is It My Breath? covers this in Chapter 9, “Breath From Below,” in a section called “Garlic’s Second Wave.” Its Breath Log records the time and what you ate, so a smell that returns three hours after lunch shows up as a pattern you can plan around. See the book.