Onion and garlic are delicious and popular ingredients that can greatly enhance a dish. Garlic, in particular, has also been linked to possible health benefits, including everything from the treatment of athlete’s foot to reducing the risk of certain types of cancer. However, both onions and garlic can cause bad breath. When a clove of garlic or onion is chopped or crushed, the compound allyl methyl sulfide (among others) is released; when ingested, this compound is absorbed into the bloodstream and can cause your sweat and breath to smell for a full day afterward.[1] [2] However, there are some strategies you can try to fight bad breath caused by onion and garlic.