Food allergy: everything you need to know about food allergies

Food allergy is an abnormal defense reaction of the body following the ingestion of food.

To find out all about allergies, see our sheet below.

Table of Contents

Food allergy, what is it?

Food-triggered reactions can occur suddenly, within 2 hours of ingestion, or delayed, up to 48 hours later. This sheet only deals with immediate reactions caused by a food allergy. To find out more about gluten intolerance, food poisoning or food sensitivities, consult our sheets dedicated to these subjects.

Food allergy is an abnormal defense reaction of the body following the ingestion of food.

Often the symptoms are mild: tingling on the lips, itching or rashes. But for some people, the allergy can be very serious and even fatal. It is then necessary to banish the food or foods in question. In France, 50 to 80 people die each year as a result of a food allergy.

Food allergies usually appear before the age of 4 years. At this age, the digestive system as well as the immune system are not yet mature, which makes it more susceptible to allergies.

There is no curative treatment. The only solution is to ban the consumption of allergenic foods.

Note: Although it is rather rare, some people react strongly to the ingestion of various food additives. The reaction can be a real allergy if the additive, even if it does not contain protein, has been contaminated by another food containing it.For example, soy lecithin, which is non-allergenic, can be contaminated with soy protein. But most often, it is a food intolerance whose symptoms resemble those of an allergy.Additives like sulphites, tartrazine and salicylates can cause an anaphylactic reaction or an asthma attack. One in 100 asthmatics is sensitive to sulphites ² .

The main allergenic foods

The most allergenic foods are not the same from one country to another. They vary in particular according to the type of food. For example, in Japan, rice allergy predominates, while in Scandinavian countries, it is more fish allergy. The following foods are responsible for about 90% of severe food allergies :

peanuts (peanuts);
shelled fruits (almonds, Brazil nuts, cashews, hazelnuts or filberts, macadamia nuts, pecans, pine nuts, pistachios, walnuts);
cow’s milk;
eggs ;
the fish ;
seafood (especially crab, lobster and shrimp);
soy le;
wheat (and related cereal varieties: kamut, spelled, triticale);
sesame seeds.

Cow’s milk allergy is the one that occurs most frequently in infants, before the introduction of solid foods. This is the case for about 2.5% of newborns .

What is an allergic reaction:

When functioning properly, the immune system detects a virus, for example, and produces antibodies (immunoglobulins or Ig) to fight it. In the case of a person allergic to a food, the immune system reacts inappropriately: it attacks a food, believing that it is an aggressor to be eliminated.

This attack causes damage, and the effects on the body are multiple: itching, redness on the skin, production of mucus, etc. These reactions result from the release of several pro-inflammatory substances: histamine, prostaglandins and leukotrienes.

Note that the immune system does not react against all the components of a food, but only against one or a few substances. It is still a protein; it is impossible to be allergic to sugar or fat.

See our Animated diagram of an allergic reaction.

In theory, allergy symptoms appear at the time of the 2nd contact with the food. At the first contact with the allergenic food, the body, more specifically the immune system, becomes “sensitized”. At the next contact, he will be ready to react. The allergy therefore develops in 2 stages.

Click to see an allergic reaction in animation

Cross Allergies

These are allergies to substances that are chemically similar. Thus, a person allergic to cow’s milk is very likely to also be allergic to goat’s milk, because of the similarity of their proteins.

Some people who know they are allergic to a particular food prefer to refrain from consuming other foods of the same family for fear that they will trigger a serious reaction.

However, it is best to consult a doctor before making such a decision, as excluding foods can create deficiencies. Skin tests can detect cross allergies.

Here is an overview of the main cross allergies.

If allergic to:	Possible reaction with:	Risk assessment:
A legume (peanut is one of them)	Another legume	5%
Peanut	A nut	35%
A nut	another nut	37% to 50%
A fish	another fish	50%
a cereal	another cereal	20%
A seafood	another seafood	75%
Cow’s milk	Beef	5% to 10%
Cow’s milk	Goat’s milk	92%
Latex (gloves, for example)	Kiwi, banana, avocado	35%
Kiwi, banana, avocado	Latex (gloves, for example)	11%

Source: Quebec Food Allergy Association

It happens that people allergic to pollen are also allergic to fresh fruits or vegetables, or to nuts. This is called oral allergy syndrome. For example, a person with a birch pollen allergy might have itchy lips, tongue, palate, and throat when eating a raw apple or carrot.

Sometimes swelling of the lips, tongue and uvula, as well as a feeling of tightness in the throat may occur. The symptoms of this syndrome are usually mild and the risk of anaphylaxis is low. This reaction occurs only with raw products since cooking destroys the allergen by modifying the structure of the protein.

Oral allergy syndrome is a form of cross allergy.

More and more frequent?

An allergy, really?

About a quarter of households believe that at least one family member has a food allergy, according to various surveys3. In reality, much less would be. This is because it is difficult to distinguish, without diagnosis, an allergy from another type of reaction to a food such as food intolerance.

Today, 5% to 6% of children have at least one food allergy. Some allergies lessen or disappear with age. It is estimated that nearly 4% of adults live with this type of allergy.

According to a report by the Centers of Disease Control and Prevention, the US government agency responsible for prevention, the prevalence of food allergies increased by 18% among those under 18 between 1997 and 2020.

The number of serious reactions would also have increased. However, as the authors of 2 studiespoint out, prevalence statistics on food allergies vary greatly from one study to another. And while there seems to be an upward trend, we can’t say for sure.

Overall, diseases of allergic origin (some cases of eczema, allergic rhinitis, asthma and urticaria) are more common today than 20 years ago.

The predisposition to allergies, called atopy in medical jargon, is said to be increasingly widespread in the West.

To what can the progression of these atopic diseases be attributed?

Food allergy: symptoms

Signs of allergies usually appear within minutes of eating the food (and up to 2 hours later).

Their nature and intensity vary from person to person. They may include any of the following symptoms, alone or in combination:

skin symptoms: itching, rashes, redness, swelling of the lips, face and limbs;
respiratory symptoms: wheezing, feeling of throat swelling, difficulty breathing, feeling of choking;
digestive symptoms: abdominal cramps, diarrhea, colic, nausea and vomiting. (If these are the only symptoms detected, it is rare that the cause is a food allergy);
cardiovascular symptoms: paleness, weak pulse, dizziness, loss of consciousness.

RemarksFor it to be a question of an anaphylactic reaction, the symptoms must be very pronounced. Usually more than one system is affected (cutaneous, respiratory, digestive, cardiovascular).For there to be anaphylactic shock, there must be a drop in blood pressure. This can lead to loss of consciousness, arrhythmia and even death.

Food allergy: how to diagnose it?

The doctor generally begins by learning about the patient’s personal and family history. He asks about the occurrence of symptoms, the contents of meals and snacks, etc.

Finally, he completes his diagnosis by performing one or other of the following tests, as appropriate.

Skin tests

A drop of a series of solutions each containing a small amount of allergen is applied to different places on the skin. Then, using a needle, the skin is lightly pricked where the extract is.

Blood tests

The UNICAP laboratory test makes it possible to measure in a blood sample the quantity of antibodies (“IgE” or immunoglobulins E) specific to a particular food.

Challenge test

This test requires the ingestion of a gradual amount of a food. It is practiced only in the hospital, with an allergist.

Food allergy: what evolution?

Allergies that tend to lessen or disappear over time: allergies to cow’s milk, eggs and soy;
allergies that tend to last a lifetime: peanut, tree nut, fish, shellfish, and sesame allergies.

Anaphylactic reaction and shock

It is estimated that 1% to 2% of the Canadian population is at risk of an anaphylactic reaction6, a severe and sudden allergic reaction. About 1 in 3 times, an anaphylactic reaction is caused by a food allergy3.

If not treated quickly, the anaphylactic reaction can progress to anaphylactic shock, i.e. drop in blood pressure, loss of consciousness and possibly death, within minutes (see symptoms below). below).

The word anaphylaxis comes from the Greek ana = opposite and phulaxis = protection, to mean that this body’s response goes against what you want.

Peanut, tree nut, fish, and shellfish allergies are most commonly implicated in anaphylactic reactions.

Vapors and odors: can they cause an anaphylactic reaction?

As a general rule, as long as there is no ingestion of the allergenic food, it is very unlikely that there will be a serious allergic reaction.

On the other hand, a person allergic to fish can present slight respiratory symptoms after having inhaled the vapors of cooking a fish, for example.

When fish are heated, their proteins become very volatile. This is why in case of fish allergy, it is not recommended to bake fish fillets and other foods at the same time, in order to avoid any contamination.

Inhaling food particles may cause an allergic reaction, but mild.

That said, most of the time, smelling the smell of a food to which one is allergic in a kitchen simply creates a reaction of disdain, without an actual allergic reaction.

Some people are at higher risk of developing a food allergy. Also, risk factors favor its appearance.

Discover them here.

Food allergy: people at risk

Children who suffer from eczema, asthma, hives or hay fever;
those of whom one or both parents also suffer from one of these forms of allergy. Only 5% to 15% of people who suffer from a food allergy have no familial predisposition;
obese children, possibly.

According to an American study involving 4,200 children, obese children are more at risk of milk allergy. The causal link between obesity and food allergies has not been demonstrated. It may be that the chronic inflammatory state present in obese people contributes to the development of allergies. There may also be a link between asthma and being overweight.

People at risk of anaphylactic reaction

People who have already had an anaphylactic reaction;
people who, in addition to having one or more food allergies, also have asthma, especially if the disease is poorly controlled;
teenagers are considered more at risk. They tend not to inform those around them of their food allergies and not to have their adrenaline (epinephrine) auto-injector with them at all times.

Remark. An unusual case shows that a food allergy can be transmitted by organ transplant ¹⁹ . A 42-year-old woman developed a peanut allergy (with anaphylactic reaction) after a liver transplant. The organ donor was allergic to this food.

Food allergy: risk factors

It is difficult to know why a food allergy appears. A few risk factors are currently being studied.

Consult our Allergies fact sheet to learn more about the factors that could explain the increase in the number of people allergic to food or other types of allergens (pollen, latex, etc.).

Certain preventive measures can be put in place to prevent the onset of food allergies.

Discover them in this sheet.

Food allergy: preventive measures

Can food allergies be prevented?

The medical community is exploring various avenues of prevention that could be of interest to parents themselves suffering from a form of allergy, whether food, respiratory or skin, and who wish to reduce the risk that their child is also allergic.

Currently, the majority of allergists agree to recommend:

no exposure to second-hand smoke in children and no smoking in adolescents;
exclusive breastfeeding up to 4 to 6 months;
introduction of solid foods according to the schedule drawn up by the paediatricians.

Other preventive means are controversial. These are hypotheses that remain to be validated.

Delay the introduction of potentially allergenic foods in children (fish, eggs, peanuts, etc.)

The idea is to give the baby the least allergenic foods first. According to the Quebec Association of Food Allergies, however, it has not been proven that this practice reduces the risk of allergy.

In general, doctors recommend introducing foods one at a time and watching for any abnormal reactions. In addition, if we wait until the child is old enough to verbally describe his discomfort, we have more possibilities of detecting possible allergies.

Consuming more omega-3s during pregnancy

Researchers believe that the high presence of omega-6 in the diet (and consequently the low presence of omega-3) could contribute to increasing the frequency of allergies of all kinds in modern societies13-15,17.

Omega-6 would make the body more sensitive to allergens and cause inflammation. Various studies have evaluated the effect of eating fatty fish or taking fish oil supplements during pregnancy, breastfeeding or early childhood on the onset of allergies in children.

According to a summary of studies, the most convincing data relate to the consumption of fish during pregnancy. A study conducted during breast-feeding showed no protective effect. For the rest, the results are contradictory.

Follow a hypoallergenic diet while breastfeeding

This fairly restrictive diet requires avoiding the main allergenic foods, such as cow’s milk, eggs and nuts, in order to avoid exposing the infant.

Note that 2 meta-analyses by the Cochrane group have concluded that this practice reduces the risk of atopic eczema in children9,18. This has been demonstrated with women who were at risk of having an allergic child (they or their spouse suffered from allergies).

The decision whether or not to follow such a diet is made on a case-by-case basis. The monitoring of such a diet must be done under the supervision of a health professional in order to avoid nutritional deficiencies in the mother.

Contraindication: this diet is contraindicated during pregnancy: it does not reduce the risk of allergy in the child and risks causing malnutrition problems in the mother and the fetus9,10.

Measures to avoid exposure to allergenic foods

Preventing allergic reactions requires constant vigilance. Finally, very small amounts of food can cause allergic reactions.

Inform those around the allergic person

The more the entourage is well informed of the child’s allergy and the measures to be taken in the event of a reaction, the better the child is protected. The entourage includes siblings, extended family, school staff, friends, parents of friends, etc.

Wear a MedicAlert® bracelet

This bracelet indicates the nature of the food allergy. It informs those around you and is very useful in an emergency.

Monitor and decode ingredient lists

The allergenic food can be found as an ingredient in a host of food products. Allergenic proteins can indeed have several names. There are about thirty for the egg (for example, livetin, lecithin and albumin), and more for milk and soy.

Identify dishes correctly

In order to avoid any confusion, the dishes intended for the allergic person should be clearly identified.

Eliminate sources of contamination

In many cases, allergic reactions are caused by the indirect ingestion of an allergenic food, through a contaminated food or kitchen utensil, for example.

How can this risk of contamination be reduced?

At home, use different utensils for preparing meals;
check the cleanliness of the dishes before using them;
reheat dishes separately for the allergic person. Allergenic proteins can indeed be found in the cooking steam of a dish;
avoid bulk foods. Contamination is frequent between the different foods offered in bulk. Consider, for example, sunflower seeds contaminated with nuts, or bulk candy contaminated with peanuts.

Restaurants, trips, buffets

These situations increase the risk of unwitting exposure to allergenic foods. More attention is needed. By choosing the least processed foods possible, the risk of being exposed to the allergen is reduced.

Schools and other public places

They should have emergency plans in place to know how to react quickly in the event that a person has a serious allergic reaction. In order to reduce the risk of contamination in kitchens and cafeterias, training is offered to staff.

No treatment can eliminate a food allergy.

To find out more, see our fact sheet on treatments below.

Food allergy: treatments

Parents who suspect a food allergy in their child should let their doctor know as soon as possible. An evaluation by an allergist may be suggested by the doctor, who can confirm an allergy using the tests described above.

No treatment can eliminate a food allergy. The only possible option is to strictly banish from your diet the food (or ingredient) that causes the allergy. For advice on this, read the Prevention section.

Some people with allergies need to carry an epinephrine auto-injector with them at all times so that they can react quickly if an anaphylactic reaction occurs. This decision to have the auto-injector with you is made with the doctor.

Treatment of anaphylactic reaction

In case of breathing problems and significant swelling, signs that indicate that an anaphylactic reaction is underway, the only medication indicated is epinephrine, also called adrenaline. It provides rapid relief of symptoms.

Epinephrine has been produced synthetically since 1900. It is obtained in the form of an injectable solution, on or without a prescription (in which case it is not reimbursed by insurance). The injection is practiced in the muscle of the thigh, on the external side.

In North America, there are two brands of epinephrine auto-injectors on the market: Epipen®, which contains a single dose, and Twinject®, which contains two. Note that the second dose of Twinject® is injected differently (see video demonstration in Sites of Interest).

In this case, the second dose may be given if symptoms are observed to worsen or not improve. You should wait 5 to 15 minutes before injecting the second dose. Usually one dose is enough.

Both brands of auto-injector come in 0.15 mg and 0.3 mg doses. The doctor will choose the dose based on the weight of the person. Adrenaline acts quickly, but its effect is short-lived, which is why a second dose is sometimes necessary.

Note that adrenaline is a hormone that the body naturally secretes in situations of stress or fear, and during physical activity. It dilates the airways, increases heart rate and constricts the small blood vessels that supply the skin and digestive system. This hormone mobilizes all the body’s resources to react quickly in an emergency situation.

What is important to know

It is very important to inform those around you of your condition (at school, at work, in leisure, etc.), which creates a safety net. You should also always carry your epinephrine auto-injector with you. You can get a case that you attach to your belt.

Also wear your MedicAlert® bracelet, if applicable. During an anaphylactic reaction, the person may not be able to seek help.

Some important information to pass on to those around you:

symptoms of an anaphylactic reaction (see Symptoms section);
how to administer adrenaline using Epipen® and Twinject® auto-injectors (see video demonstrations in the Sites of Interest section).

How to react ?

When you detect an anaphylactic reaction, act quickly;
administer the dose of adrenaline contained in the auto-injector;
call emergency medical services (9-1-1);
if the symptoms do not improve after the first injection of adrenaline and you have not yet obtained medical help, you can inject a second dose of adrenaline (the second dose of Twinject®, if necessary) 5 to 15 minutes after the first injection;
doctors will monitor the patient’s condition for at least 4 hours to ensure that the reaction is over6. It has happened in the past that attacks have become exacerbated after a few hours, without further exposure to the allergen.

After using an auto-injector, you should take the empty auto-injector device to a pharmacist and get a new one. Furthermore, epinephrine is sensitive to light and air. Watch the product expiration date.

In an emergency, doctors advise using epinephrine first. Other medications, such as antihistamines or bronchodilators (commonly used by people with asthma), have no effect on an already severe reaction. Ask your doctor.

Important: note that taking beta-blocker drugs, used for example to treat hypertension, reduces the effectiveness of adrenaline. These drugs are contraindicated in people requiring an adrenaline auto-injector.

Nutrition advice

To manage the changes in diet caused by a food allergy and to find substitutes and recipes without allergens, the advice of a nutritionist can be very useful.

She can also assess whether taking dietary supplements is necessary. Associations dedicated to food allergies can also be useful.

Remark. Some forms of allergies (allergic rhinitis, insect venom allergy) can decrease in intensity thanks to desensitization treatment.Performing this type of treatment in cases of severe food allergy is very dangerous, as it involves exposing the allergic person to increasing doses of the allergen. Indeed, the ingestion of a tiny dose of allergenic food can trigger a potentially fatal anaphylactic shock.The only safe way to check that a food allergy has diminished or disappeared is to do a medical skin reaction test or measure the food’s own immunoglobulins (antibodies) in the blood.

As part of its quality approach, Passeportsanté.net invites you to discover the opinion of a health professional.

Dr. Dominic Larose, emergency physician, gives you his opinion on food allergies.

Food allergy: our doctor’s opinion

“Living with a food allergy is complicated. You have to learn the many variations of the not always clear names of foods on the labels. It’s a real headache.

There are still people who die as a result of a food allergy which was however known. Without exception, anyone who knows they have a serious allergy must have adrenaline in their possession.

And if a person begins to show symptoms of a severe allergy, they should be helped by contacting the emergency services (9-1-1) immediately!

There are also all those who, having had an illness X shortly after eating a food Y, start eliminating one food after another, believing they are having an allergic reaction when this is not the case. So they’re eliminating a lot of healthy foods that they shouldn’t be depriving themselves of.”

Dr Dominic Larose, M.D.

In the event of food allergies, certain complementary approaches make it possible to treat them in a more natural way.

Check out the list here.

Food allergy: complementary approaches

Based on our research, there is no evidence regarding the effectiveness of complementary approaches to treating or reducing allergic reactions to foods.

Caution. Experiencing a treatment and then attempting to reintroduce the allergenic food in order to assess whether that treatment is effective can be dangerous, even fatal, in someone with severe food allergies.

For these reasons, we should mention that the Ordre des acupuncteurs du Québec prohibits its members from treating “a serious allergy problem leading to a violent reaction or even an anaphylactic shock, such as food allergy”.

Food allergy is an abnormal defense reaction of the body following the ingestion of food.

To find out all about allergies, see our sheet below.

Food allergy: what evolution?

Allergies that tend to lessen or disappear over time: allergies to cow’s milk, eggs and soy;
allergies that tend to last a lifetime: peanut, tree nut, fish, shellfish, and sesame allergies.

Anaphylactic reaction and shock

The word anaphylaxis comes from the Greek ana = opposite and phulaxis = protection, to mean that this body’s response goes against what you want.

Peanut, tree nut, fish, and shellfish allergies are most commonly implicated in anaphylactic reactions.

Vapors and odors: can they cause an anaphylactic reaction?

As a general rule, as long as there is no ingestion of the allergenic food, it is very unlikely that there will be a serious allergic reaction.

On the other hand, a person allergic to fish can present slight respiratory symptoms after having inhaled the vapors of cooking a fish, for example.

Inhaling food particles may cause an allergic reaction, but mild.

That said, most of the time, smelling the smell of a food to which one is allergic in a kitchen simply creates a reaction of disdain, without an actual allergic reaction.