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Food allergy: all you need to know about food allergies
Food-triggered reactions can occur in ways sudden, within 2 hours of ingestion, or so delayed, up to 48 hours later. This sheet deals only with immediate reactions caused by allergies to a food. To find out more about gluten intolerance, food poisoning or food sensitivities, consult our sheets dedicated to these subjects. |
THEfood allergy is an abnormal reaction of body defense following the ingestion of a food.
Often the symptoms are mild: tingling on the lips, itching or rash. But for some people, the allergy can be very serious and even deadly. We must then ban 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. At this age, the digestive system as well as the immune system is 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 proteins. But most often it is a Food intolerance whose symptoms resemble those of an allergy. Additives like sulfites, tartrazine, and salicylates can cause an anaphylactic reaction or asthma attack. One in 100 people with asthma are sensitive to sulphites2. |
Symptoms of food allergy
The signs of allergies usually appear within minutes of eating the food (and up to 2 hours after).
Their nature and intensity vary from person to person. They can include any of the following symptoms, alone or in combination.
- Skin symptoms : itching, rash, redness, swelling of the lips, face and limbs.
- Respiratory symptoms : wheezing, a feeling of swelling in the throat, difficulty in breathing, a feeling of suffocation.
- Digestive symptoms : abdominal cramps, diarrhea, colic, nausea and vomiting. (If these are the only symptoms detected, it is rare for the cause to be a food allergy.)
- Cardiovascular symptoms : pallor, weak pulse, dizziness, loss of consciousness.
Remarks
- So that it is a question of anaphylactic reaction, the symptoms should be very pronounced. Usually more than one system is involved (cutaneous, respiratory, digestive, cardiovascular).
- So that it is a question of a anaphylactic shock, there must be a drop in blood pressure. This can lead to unconsciousness, arrhythmia and even death.
Diagnostic
The doctor usually begins by learning about the patient’s personal and family history. He asks questions about the occurrence of symptoms, the content of meals and snacks, etc. Finally, he completes his diagnosis by carrying out one or other of the tests following, as the case may be.
- Skin tests. A drop of a series of solutions each containing a small amount of the allergen is applied to different places on the skin. Then, using a needle, lightly prick the skin where the extract is located.
- Blood tests. The UNICAP laboratory test measures the amount of antibodies (“IgE” or immunoglobulin E) specific to a particular food in a blood sample.
- Provocation test. This test requires the ingestion of a gradual amount of a food. It is performed only in the hospital, with an allergist.
The main allergenic foods
The foodstuffs most allergens are not the same from one country to another. They vary in particular according to the type of food. For example, at Japan, rice allergy predominates, while in Scandinavian countries, it is rather fish allergy. At Canada, the following foods are responsible for about 90% of severe food allergies4 :
- 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;
- wheat (and parent varieties of cereals: kamut, spelled, triticale);
- sesame seeds.
Allergy to cow milk is that which occurs most frequently in infants, before the introduction of solid foods. This is the case for about 2,5% of newborns1.
What the allergic reaction is 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 eliminate. This attack causes damage, and the effects on the body are manifold: itching, redness on the skin, mucus production, 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 always a protein; it is impossible to be allergic to a sugar or a fat. See our Animated Diagram of an Allergic Reaction. In theory, allergy symptoms appear around the time of 2e contact with the food. At the first contact with the allergenic food, the body, more specifically the immune system, is “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
This is’allergies to substances that are chemically similar. Thus, a person allergic to cow’s milk is likely to be also allergic to goat’s milk, due to the similarity of their protein.
Some people who know they are allergic to a particular food prefer not to consume other foods of the same family for fear that they trigger a serious reaction. However, it is best to consult a doctor before making such a decision, as excluding foods can create deficiencies. From skin tests allow to discover 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% |
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 Association of Food Allergies
Sometimes people who are allergic to pollen are also allergic to fresh fruits or vegetables, or to nuts. This is called the oral allergy syndrome. For example, a person allergic to birch pollen might get itchy lips, tongue, palate, and throat when they eat an apple or raw 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 ofanaphylaxis is weak. This reaction only occurs with raw products since cooking destroys the allergen by changing the structure of the protein. Oral allergy syndrome is a form of cross allergy.
Evolution
- Allergies that tend to improve or disappear over time: allergies to cow’s milk, eggs and soy.
- Allergies that tend to persist for life: allergies to peanuts, tree nuts, fish, seafood and sesame.
Anaphylactic reaction and shock
It is estimated that 1% to 2% of the Canadian population is at risk of reaction anaphylactic6, a severe and sudden allergic reaction. About 1 in 3 times, the anaphylactic reaction is caused by allergies alimentary3. If not treated promptly, 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 response of the body goes against what we want.
Allergies to peanuts, to noix, to fish and sea food are most often involved 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 could be a serious allergic reaction. On the other hand, a person allergic to fish may have mild respiratory symptoms after breathing the cooking vapors of a fish, for example. When you heat the fish, its proteins become very volatile. Therefore, in the event of a fish allergy, it is not recommended to cook fish fillets and other foods in the oven at the same time, in order to avoid contamination. Inhaling food particles can cause an allergic reaction, but mild However, most of the time, smelling the smell of a food you are allergic to in a kitchen simply creates a reaction of disdain, without a real allergic reaction. |
More and more frequent?
An allergy, really? About a quarter of households believe 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. |
Nowadays, 5% to 6% of children have at least one food allergy3. Some allergies get better or go away with age. It is estimated that nearly 4% of adults live with this type of allergy3.
According to a report from 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 the age of 18, between 1997 and 200720. The number of serious reactions is also said to have increased. However, as the authors of 2 studies published in 2010 point out21,22, prevalence statistics for food allergies vary greatly from study to study. And while there appears to be an upward trend, it cannot be said for sure.
Overall, diseases of origin allergic (some cases of eczema, allergic rhinitis, asthma and urticaria) are more common today than twenty years ago. The predisposition to allergies, called atopy in medical jargon, would be more and more widespread in the West. To what can we attribute the progression of these atopic diseases?