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 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, someone with a birch pollen allergy might experience 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 3 .
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 200720.
The number of serious reactions would also have increased. However, as the authors of 2 studies point 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 swelling in the throat, difficulty in 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 allergy.
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 mild respiratory symptoms after having inhaled the cooking fumes of 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 at greater 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 . 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 estimate 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 societies.
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 follow-up 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.
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.
In addition, you can find ingredients that you would not expect in some prepared products, such as dairy products in deli meats or fish in barbecue sauce (Worcestershire sauce contains anchovies).
We should mention that peanuts, almonds, cow’s milk and eggs are the only allergens for which we have recognized detection methods. In Quebec, the Certified Allergen Control Program, launched by the Quebec Association of Food Allergies in 2006, offers an independent assessment of products certified free of any of these allergens.
See the Sites of Interest section to learn more about this program.
It is important not to consume products that “may contain traces” or “contain traces” of the allergen in question. It is useful to know that, for the moment, the Canadian and French regulations in terms of labeling do not oblige the agri-food industries to display this mention.
In addition, it happens that there are slight variations in the composition of a product from one batch to another, or that the recipes are modified. With prepared foods, you have to learn to manage the risk. Chocolate, cookies and breakfast cereals are most likely to contain traces of peanuts.
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.
