Dr. Scott Sicherer: The answer would depend upon the amount of protein in the steam, your personal degree of sensitivity, whether you have asthma, and the amount inhaled.

The amount inhaled is related to proximity, room size, ventilation and other factors. This issue has not been extensively studied.

One small study attempted to replicate reported allergic reactions to cooking vapors in food-allergic children with asthma by having the children in a 7- by 13-foot room while food was being cooked on a stovetop for 20 minutes. Reactions were replicated in five of nine children.

In those five children, the triggers were fish (three children), chickpea and buckwheat. The four negative tests were to milk (two), fish and egg. Among the five reactions, all the children had asthma symptoms and two also developed hives (chickpea and buckwheat).

Regarding your shellfish allergy, based on the study mentioned and studies of people with occupational asthma related to working with shellfish, it seems clear that shellfish protein can become airborne in steam and may trigger reactions. Therefore, steam coming from plates of hot shellfish could pose a risk.

Dr. Scott Sicherer is Chief of the Division of Allergy and Immunology of the Jaffe Food Allergy Institute at the Mount Sinai School of Medicine in New York. Together with Dr. Hemant Sharma, Associate Chief of the Division of Allergy and Immunology at Children’s National Medical Center in Washington, he writes “The Food Allergy Experts” column in the American Edition of Allergic Living magazine. Questions submitted below will be considered for answer in the magazine.

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.