Food allergy reactions primarily occur via ingestion. Reactions to allergens can occur when the allergen comes into contact with your mucus membranes, which line the mouth, eyes, and nose. If you are in the same room as your food allergen and you happen to get some of that allergen on yourself, you can have an allergic reaction by touching your mouth, eyes, or nose. Some allergens can also become airborne when cooking. Shellfish is a good example of an allergen whose proteins can become airborne when cooking.9 If the allergens land on the mouth, eyes, and nose, they can trigger an allergic reaction.