Garlic is part of the onion family (Allium family) and so people who are allergic to garlic can also react to onions, shallots, leeks, asparagus and chives. There are also similarities between the allergens (proteins that cause allergies) in onions and the pollens of plants from the Phleum (catstail or timothy grass) and Chenopodium (goosefoot) families; those with hayfever may be more likely to suffer from garlic allergy!
Garlic is available in many different forms including flakes, powder, garlic salt, garlic extract, juice and garlic tablets.