Fresh parsley, citrus peels and lemon juice all work to combat onion breath. Proper oral hygiene, including flossing, brushing and using mouthwash after eating onions is also helpful.
Fresh sprigs of parsley sweeten the breath, which helps to eliminate the onion odor. After eating onions, chew on a fresh sprig or two to lessen the odor. Couple lemon juice with equal parts cool water and make sure to swish it around well in the mouth similar to using a mouthwash. Citrus peels have a strong scent and flavor, which helps them to overpower the scent and flavor of an onion.