Dr. Susan Waserman: Most food allergies start in childhood, but you’re right, they can develop at any time in a person’s life.

Factors that favour the development of food allergy in adults include sensitization to pollens and house dust mites, as well as occupational sensitization (which occurs when people who regularly handle and inhale food become sensitized to it due to repeated exposures).

As well, adults with birch pollen allergy may develop “oral allergy syndrome,” which leads those affected to experience itchy mouth when they eat certain raw fruits and vegetables. This is the result of cross-reactivity between the food and the pollen.

Interestingly, those sensitized to house dust mites may end up with shrimp allergy because both contain the protein tropomyosin.

Occupational sensitization is also associated with crab and pork allergies.

Dr. Susan Waserman is an allergist and Professor of Medicine in the Division of Allergy and Clinical Immunology at McMaster University in Hamilton, Ont. She is also a past president of the Canadian Society of Allergy and Clinical Immunology.

We welcome your question to Allergic Living’s Ask the Allergist. Thank you for understanding that the specialists aren’t able to answer every question received.

He was diagnosed with the food allergies when he was 9 months old, and has no recollection of getting sick from the foods. I think he is getting curious, trying to experiment, and I am worried about him at school. Do you have any suggestions about dealing with his curious nature?

Dr. Scott Sicherer: You are describing behaviors that represent age-appropriate natural curiosity and some element of “testing boundaries”. I recommend responding the same way you would if he attempted other dangerous actions such as running into the street or playing with electric sockets. In other words, take stronger actions to ensure he does not eat the avoided food, including extra supervision and placing temptations out of reach.

Reasoning with a 5-year-old about the consequences of the actions is not likely to be fruitful, although it is appropriate to say “Eating the food could make you sick and we don’t want you to get sick.”

Assuming a child is otherwise developmentally normal, positive reinforcement for appropriate behavior may be helpful, including verbal praise (“We are so proud of our big boy for not touching those cookies”) or a sticker chart (“Look, you got two stickers for twice not touching those cookies and eating your safe ones instead. Now you can choose a special toy to play with”).

One exercise you can try: Ask an adult friend to offer your son food and teach him to say, “No thanks, I have an allergy and my mom or dad has to make sure it is OK.” Provide positive reinforcement when he does a good job. Reading stories
about children with food allergies and pointing out how others have restrictions may help him understand and accept the differences, but also recognize that he is mostly doing the same things as others.

Next: Sending a curious food-allergic child to school

Dr. Hemant Sharma: This is a great question, and one that many parents of children with cow’s milk allergy have as they search for a suitable substitute for cow’s milk. Unfortunately, because goat’s milk protein is similar in structure to cow’s milk protein, more than 90 percent of  the time, the immune system will mistake the two and cause a reaction to goat’s milk or goat’s cheese in someone with a cow’s milk allergy. So goat’s milk is not a safe alternative to cow’s milk, and for the same reason, neither are sheep’s milk nor buffalo’s milk.

You can discuss with your child’s allergist what might be an acceptable cow’s milk substitute. An option for an infant would be an extensively hydrolyzed, cow’s milk-based formula, in which the cow’s milk protein is extensively broken down, making it less recognizable by the immune system and less likely to cause a reaction. Since these formulas are also good sources of nutrients, many allergists will recommend children on restricted diets remain on them beyond the age of one year.

Once ready to wean from a formula, options at that point might include soy milk or rice milk, assuming your child does not also have allergies to those foods. To be sure that all nutritional requirements are being met, it definitely is a good idea to discuss your options with your child’s allergist or a dietitian.

Dr. Sharma is an allergist, clinical researcher and Assistant Professor of Pediatrics. He is Associate Chief of the Division of Allergy and Immunology at Children’s National Medical Center in Washington D.C. and Director of the Food Allergy Program. He is also the site director for the National Institutes of Health Allergy and Immunology fellowship program. 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. Scott Sicherer: You are not alone in developing shrimp allergy as an adult. In our U.S. prevalence studies and studies in Canada that tracked peanut, tree nut, fish, shellfish and sesame allergies, shellfish was the most common self-reported allergy.

We know food allergies are affected by the immune system, heredity, environmental factors, and the characteristics of the foods themselves. We know that many food allergies are outgrown, so there are clearly differences between children and adults. What we are missing are the exact details underlying each factor and how the factors interrelate. We only have theories to address your question.

The characteristics of food proteins likely play a role. Proteins responsible for persistent and severe allergies are more resistant to digestion and more likely to be recognized by the immune system. It may be that the child’s immature gut or immune system is more prone to attack the proteins, but shrimp may be an example of a protein that is particularly capable of triggering an immune attack even for adults.

A route of exposure other than through the mouth may be a contributing problem for adult-onset allergy. Most food allergies that begin beyond childhood are mild reactions to raw fruits and vegetables. This type of allergy is called oral allergy syndrome and is related to proteins in pollens. For example, apple shares similar proteins with birch pollen. Thus, becoming allergic to similar proteins in the air starts the trouble. A theory has also been proposed that environmental exposure to peanut, without actually eating peanut, may increase the risk of peanut allergy. Interestingly, shellfish proteins are similar to ones found in dust mite and cockroach, although most people with those allergies tolerate shellfish.

Next: Digestion Changes

Dr. Watson: There are many factors that contribute to the development of asthma in children. Having a mother or father with asthma is only one of the risk factors.

There are studies looking at an index called the Modified Asthma Predictive Index. In children with three or more wheezing episodes, one of which is documented by a physician, major risk factors include family history, personal history of allergy and allergies to inhalant allergens.

You also ask whether taking precautions will prevent asthma. There isn’t enough evidence to support any recommendations. For example, exposure to pets in children has been  protective in some studies, yet contributed to the onset of asthma in other studies. For children who developed asthma or hay fever, month of birth seemed a risk factor.

The bottom line is that these are things you really cannot control. If you have pets, there is not enough evidence to say to keep or get rid of them. The only option would be if your child develops symptoms around the pets, then you should give them away.

As far as the springtime, there are no special precautions to protect your child. Watch instead for early symptoms and, should you have concerns, speak to your doctor. As a father of an 18-year-old and a 22-year-old (and an empty-nester), the most important piece of advice I can give you is to relax and enjoy your child.

We welcome your question to Allergic Living’s Ask the Allergist. Thank you for understanding that the specialists aren’t able to answer every question received.

Dr. Wade Watson is a pediatric allergist and Professor of Pediatrics at Dalhousie University. He is also the head of the Division of Allergy at the IWK Health Centre in Halifax.

Dr. Sicherer: The allergic form of eczema, also known as atopic dermatitis, is related to other allergic illnesses including asthma, allergic rhinitis (hay fever) and food allergies. These illnesses are inherited and often occur together in the same person.

Infants and children who are known to be allergic to milk are more likely to have atopic dermatitis and other allergies. Infants with atopic dermatitis are more likely to have positive allergy tests to milk as well as other food and environmental allergens such as dust mite and cat dander.

Milk allergy is not necessarily directly linked with the eczema, but both are more likely to occur in allergy-prone individuals.

The more severe the allergic skin rash and the earlier the onset, the greater the chance that the infant may have, or develop, other allergies, including food allergies. Again, this probably reflects a person’s general allergic inclination, rather than being a direct link between a food and the skin rash.

But could there be a direct link between allergy and eczema? One theory is that the broken, rashy skin allows proteins to be “seen” by the immune system, while normal skin keeps out the allergens. This might make it easier for the immune system to attack the proteins that land on the broken skin, causing more allergies. However, this is just a theory.

Next: One direct link between eczema, milk allergy

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.