courierpress asked a bunch of food scientests about what makes garlic so smelly and onions so tear-inducing:
One of the reasons garlic breath is so strong is it’s “full of sulfurous compounds that ‘feed’ the bacteria in the mouth, and bad breath (halitosis) is caused as a result,” says Gerard E. Mullin, M.D., M.H.S., the director of gastroenterology at Johns Hopkins Hospital. However, the more relentless bad breath associated with garlic originates in the intestinal tract.
“Sulfur-containing gases from the garlic are produced in the intestines and are only slowly eliminated by metabolism,” says Pintauro.
LaBorde also notes that the chemical responsible for garlic breath enters the bloodstream and circulates. And, “The volatile garlic compounds diffuse from the blood to the air deep within the lungs, and we breathe them out.”