While allergists stress that severe reactions to airborne food particles are extremely uncommon, there are some instances in which allergenic food proteins can get into the air and potentially cause trouble.

According to Dr. Scott Sicherer of the Jaffe Food Allergy Institute at Mount Sinai School of Medicine in New York, foods with proteins that are stable to cooking can get into the air during heating – and if they then get into the airways of someone who has a severe enough allergy to that food, they can lead to allergic symptoms.

For instance, allergic persons who are exquisitely sensitive to fish or shellfish can react to tiny aerosolized proteins that float in the air when seafood is being fried, steamed or boiled. There may be an increased risk of this in seafood restaurants where large quantities are being prepared and served piping hot.

In fact, airborne reactions are not just a concern for the seafood allergic. Commonly fried foods such as eggs, and powdery forms of some foods can cause similar problems if they get kicked up into the air.

Dried egg powder, soy flour and wheat flour are common culprits behind airborne food reactions, and some people who are able to eat wheat can get respiratory symptoms when they inhale it – a condition that is not uncommon in food processing and has been dubbed “Baker’s Asthma”. A similar condition called “Crab Asthma” is prevalent in the fish processing industry.

Sicherer says that some foods are less likely to get aerosolized – for example, oily and inert peanut butter – which is why they don’t present as much of an airborne danger.

Symptoms from aerosolized food proteins can range from hives and itching to more serious effects including asthma – but Sicherer strongly emphasizes that the risk of anaphylaxis from exposure to airborne food allergens is very low.

Bottom line: Small exposures to inhaled allergens are not usually a problem, but more significant exposures should be avoided. If you’re allergic to seafood, walking past a fish shop or a seafood restaurant likely won’t cause any harm; but sitting in a seafood restaurant for a long period may have you saying, “Check please!”

Dr. Ham Pong: You can be assured that anaphylaxis to airborne food particles is very rare. An allergic reaction to food will not occur because someone is eating it in a classroom or vicinity of the allergic person. The main reason for advising that the allergenic food not be brought into a classroom is the potential for an allergic child to accidentally ingest some by sharing food. Secondary reasons (less likely to cause anaphylaxis because of the smaller quantities involved) are cross-contamination of desks, toys etc.

The smell of peanut/nuts or peanut butter does not come from the peanut protein, and therefore allergic reactions should not occur just because you smell peanut or because there is an open jar of peanut butter in the area.

Allergic reactions to peanut occur mostly when the peanut enters the body, either by licking it, tasting it or eating it – for instance, bringing it to your lips, mouth directly, or indirectly by transferring it from your hands or other people’s lips to your mouth or eyes. Therefore, it is important to realize that severe allergic reactions or anaphylaxis to peanut generally occur with eating or tasting peanut, and not by touching or smelling it.

In fact, the smell of peanut should cause no allergic reactions at all, but may make a peanut allergic person feel very uncomfortable because he or she is smelling something that is distasteful and potentially dangerous if eaten. It is likely a defense mechanism to warn the peanut allergic person to move away from the area, in case they do get into contact with the peanut accidentally.

The only exception to the above is if peanut protein itself is in the air that you breathe. If a peanut allergic person breathes enough of the peanut protein in the air, the person can have a serious allergic reaction, asthma attack or anaphylaxis. Situations in which this can occur are unusual but can happen. For instance, if a large number of people are opening packages of peanut at the same time – e.g. when peanut packages served on an airplane – and the peanut protein dust gets into the air in an enclosed space.

Other examples would be boiling or frying a food with peanut, as minute peanut particles can then get into the air [through steam or oil particles carrying peanut protein]. Another example could be a floor with large amounts of peanut shells and containing peanut dust where people walking on the shells can stir up peanut dust in the air. (An example would be sports bars.)

However, remember that these reactions might occur only in an enclosed area and with large amounts of peanut dust stirred up in the air, and should not occur with a few peanut shells scattered on the ground, or with one or two people eating peanut next to you. Allergy to inhaled food proteins is rare and may occur in unusual cases. However, it has been reported in some individuals to peanut, wheat, milk, egg, soy, fish, crab.

Dr. Antony Ham Pong is a pediatric allergist practising in Ottawa.