Contents
Allergies (overview)
Allergies: what are they?
Allergy, also called hypersensitivity, is an abnormal reaction of the immune system against elements foreign to the body (allergens), but harmless. It can appear in different regions of the body: on the skin, in the eyes, in the digestive system or in the respiratory tract. The types of symptoms and their intensity will vary depending on where the allergy starts, and several other factors that are unique to each person. They can be very inconspicuous, such as the appearance of redness on the skin, or potentially fatal, such as shock anaphylactic.
The main types of allergic manifestations are:
- food allergies;
- asthma, at least in one of its forms, allergic asthma;
- atopic eczema;
- allergic rhinitis;
- certain forms of urticaria;
- anaphylaxis.
People who are allergic to a single allergen are rarely allergic. The allergic reaction can manifest itself in several ways in the same person; allergic rhinitis has been shown to be a risk factor for the development of asthma15. Therefore, pollen desensitization treatment to treat hay fever can sometimes prevent asthma attacks caused by exposure to these pollens.1.
The allergic reaction
In most cases, the allergic reaction requires 2 contacts with the allergen.
- Awareness. The first time the allergen enters the body, through skin or by the mucous membranes (eyes, respiratory or digestive tract), the immune system identifies the foreign element as dangerous. He begins to make specific antibodies against him.
The antibody, or immunoglobulins, are substances made by the immune system. They recognize and destroy certain foreign elements to which the body is exposed. The immune system produces 5 types of immunoglobulins called Ig A, Ig D, Ig E, Ig G and Ig M, which have specific functions. In people with allergies, it is especially Ig E that is involved. |
- The allergic reaction. When the allergen enters the body a second time, the immune system is ready to respond. Antibodies seek to eliminate the allergen by triggering a set of defense reactions.
| |
| |
Click to see the animation |
IMPORTANT The anaphylactic reaction. This allergic reaction, sudden and generalized, affects the whole organism. If not treated quickly, it can progress to anaphylactic shock, that is, drop in blood pressure, loss of consciousness and possibly death, within minutes. As soon as the first signs of serious reaction – swelling in the face or mouth, heartache, red patches on the body – and as soon as possible before the first ones appear signs of respiratory distress -difficulty in breathing or swallowing, wheezing, modification or disappearance of the voice-, one must administer epinephrine (ÉpiPen®, Twinject®) and go to the emergency room as quickly as possible. The atopy. Atopy is an inherited predisposition to allergies. A person can suffer from several forms of allergies (asthma, rhinitis, eczema, etc.), for reasons that are not known. According to the International Study of Asthma and Allergies in Children, a large study conducted in Europe, 40% to 60% of children with atopic eczema will suffer from respiratory allergies, and 10% to 20 % will have asthma2. The first signs of allergy are often atopic eczema and food allergies, which can appear in infants. Symptoms of allergic rhinitis – sniffling, eye irritation, and nasal congestion – and asthma occur somewhat later in infancy.3. |
Causes
For there to be an allergy, 2 conditions are essential: the body must be sensitive to a substance, called an allergen, and this substance must be in the person’s environment.
The most common allergens are :
- from airborne allergens : pollen, mite droppings and pet dander;
- from food allergens : peanuts, cow’s milk, eggs, wheat, soy (soy), tree nuts, sesame, fish, shellfish and sulphites (a preservative);
- other allergens : drugs, latex, insect venom (bees, wasps, bumblebees, hornets).
Allergic to animal hair? We are not allergic to hair, but to animal dander or saliva, no more than we are to pillow feathers and quilts, but rather to the droppings of the mites that hide there. |
We still know little about theorigin of allergies. Experts agree that they are caused by a variety of factors. Although there are several cases of family allergies, the majority of children with allergies come from families with no history of allergies.4. Therefore, although there is a genetic predisposition, other factors are involved, among which: tobacco smoke, the western way of life and the environment, especially air pollution. Stress can cause allergy symptoms to appear, but it is not directly responsible.
Milk: allergy or intolerance? Cow’s milk allergy caused by certain milk proteins should not be confused with lactose intolerance, an inability to digest this milk sugar. Symptoms of lactose intolerance can be eliminated by consuming lactose-free dairy products or by taking supplements of lactase (Lactaid®), the enzyme deficient, when consuming dairy products. |
More and more frequent
Allergies are much more common today than they were 30 years ago. In the world, the prevalence of allergic diseases has doubled in the past 15 to 20 years. 40% to 50% of the population in industrialized countries is affected by some form of allergy5.
- In Quebec, according to a report produced by the National Institute of Public Health of Quebec, all types of allergies experienced a significant increase from 1987 to 19986. The prevalence of allergic rhinitis increased from 6% to 9,4%, theasthma, from 2,3% to 5% and other allergies from 6,5% to 10,3%.
- While at the beginning of the XXst century, allergic rhinitis affected about 1% of the population of Western Europe, nowadays the proportion of people affected is 15% to 20%2. In some European countries, almost 1 in 4 children aged 7 or younger haveeczema atopic. In addition, more than 10% of children aged 13 and 14 suffer from asthma.
What to attribute the progression of allergies to? By observing the social and environmental changes that have marked the last decades, researchers have advanced various hypotheses. The hygienist hypothesis. According to this hypothesis, the fact of living in an environment (houses, workplaces and leisure activities) that is increasingly clean and sanitized would explain the increase in the number of cases of allergies in recent decades. Contact, at an early age, with viruses and bacteria would allow a healthy maturation of the immune system which, otherwise, would tend to have an allergic reaction. This would explain why children who contract four or five colds a year are less at risk of allergies. The permeability of the mucous membranes. According to another hypothesis, allergies would rather be the consequence of too great a permeability of the mucous membranes (gastrointestinal, oral, respiratory) or of a modification of the intestinal flora. For more on the subject, read Allergies: What the Experts Say. |
Evolution
Food allergies tend to persist: you often have to ban the food from your diet for the rest of your life. As for respiratory allergies, they can subside to the point of disappearing almost completely, despite the presence of the allergen. It is not known why a tolerance can set in, in this case. Atopic eczema also tends to get better over the years. On the contrary, allergies to insect venom that occur following bites can get worse, sometimes after the second bite, unless you receive desensitization treatment.
Diagnostic
The doctor takes a history of the symptoms: when do they appear and how. Skin tests or a blood sample make it possible to precisely discover the allergen in question in order to eliminate it as much as possible from its living environment, and to be able to better treat the allergy.
The skin tests identify the substances that trigger the allergic reaction. They consist in exposing the skin to very small doses of purified allergenic substances; you can test about forty at a time. These substances can be pollen from various plants, mold, animal dander, mites, bee venom, penicillin, etc. The signs of an allergic reaction are then observed, which can be immediate or delayed (48 hours later, especially for eczema). If there is an allergy, a small red dot appears, similar to an insect bite.