Food allergies: causes and symptoms
Food allergies are an abnormal response of the immune system to one or more foods or food components
The allergen, that is, the substance that triggers this abnormal response, is in almost all cases, a protein.
Ninety percent of food allergies are caused by a group of eight foods: cow’s milk, eggs, soy, cereals, peanuts and other nuts, fish and shellfish.
What makes food allergies so difficult to manage is that the substance or substances to which one is allergic are not isolated but can be found in everyday foods.
Generally, food allergies appear in the first ten years of life, the period of immune system development.
Indeed, some allergies are triggered as early as the first few months of life, during breastfeeding, as a result of an immune response triggered by proteins in breast milk.
Types of food allergies
The “Top 8” allergenic foods result in as many types of Allergy of plant and animal origin:
Plant-derived allergies:
- Allergy to peanuts: peanuts are one of the most common food allergens that usually results in a severe and chronic form of allergy.
- Allergy to other nuts: the main nuts involved in allergic reactions are almonds, hazelnuts, walnuts, cashews, and pistachios.
- Soy allergy: soy allergy is an immune response to at least one of sixteen potentially allergenic soy proteins.
- Wheat allergy: wheat allergy can result from the production of specific IgE against several classes of proteins that are still “toxic” after cooking or common technological treatments.
Allergies of animal origin:
- Egg allergy: this is one of the most common food allergies in infants and children.
- Allergy to shellfish (crab, lobster, shrimp): allergy to shellfish is an adverse immune reaction to certain proteins in these foods.
- Allergy to fish: as with shellfish allergy, allergy to fish results in an adverse immune reaction to certain proteins in the food.
- Cow’s milk allergy: cow’s milk protein allergy affects between 2% and 3% of children generally before the age of 3 years and peaking between the first 3 to 5 months.
Causes of food allergies and risk factors
The main cause of food allergies is “loss of neutrality” toward food.
To prevent the absorption of potentially pathogenic and dangerous agents from food and at the same time to ensure tolerance, i.e., “neutrality” of the immune system toward dietary proteins and “good” (so-called commensal) bacteria, precise immune mechanisms exist at the gastrointestinal level.
The normal “tolerance” of the immune system toward food antigens may fail, in some situations, toward one or more allergenic proteins in foods, establishing a food allergy.
The tendency to develop it depends on heredity and other factors (viral gastroenteritis, premature birth).
But environmental factors, such as air pollution, exposure to cigarette smoke in childhood (or during the mother’s pregnancy), and being in humid environments can also contribute.
In some people, the allergic reaction may be triggered by exercise, with itching and lightheadedness immediately after starting a workout at the gym or a run.
Not eating for a couple of hours before exercise and avoiding “suspect” foods can help prevent this problem.
In recent years a significant increase in allergic diseases has been observed (to give an example of the growth rate of these allergies, in Great Britain alone, from 1990 to 2007 they increased by 500%!) especially food allergy, which has taken on the characteristics of a real epidemic, to the point of making life difficult for 6-8 % of children under 3 years of age (more than 10% if even mild reactions to fruits and vegetables are considered) and up to 3% of adults.
Children represent the category most susceptible to food allergies because their bodies, especially when very young, are still in formation: the gastrointestinal system, which is supposed to block antigens, especially in infants, is not yet well developed and may fail in this function, causing allergic reactions that usually affect the respiratory system (with asthma and conjunctivitis), the gastrointestinal system (with diarrhea, abdominal pain and vomiting) and the skin (with hives and eczema).
About 85 percent of children with food allergies spontaneously recover in the first 3 to 5 years of life, although persistence into adulthood becomes increasingly common.
However, predisposition to allergies is a determining factor: if one parent is already allergic, the child will have about a 45% chance of also developing food allergies; the percentage rises almost twice as high, to about 80%, if both parents are allergic.
It is therefore important, especially in these children with genetic predisposition, to prolong breastfeeding as much as possible, which allows them to take advantage of maternal antibodies.
Signs and symptoms of food allergies
Symptoms of food allergy usually develop a few minutes to two hours after eating the “offending” food.
For some, the allergic reaction to a particular food may be only “unpleasant,” but not severe.
For others, however, it can also be very serious and life-threatening.
Common signs and symptoms include:
– tingling or itching sensation in the mouth
– hives, itching or eczema on the body
– swelling of the lips, face, tongue and throat or other parts of the body
– wheezing, nasal congestion or breathing problems
– abdominal pain, diarrhea, nausea or vomiting
– dizziness, lightheadedness or fainting.
Anaphylactic shock, is an extreme and potentially very dangerous reaction that can occur in some people and in special cases (fortunately rare).
In people with allergies, it is always necessary to keep in mind the possibility of such a reaction occurring.
It is necessary to know how to recognize it early so that immediate action can be taken.
Symptoms of anaphylactic shock include:
- constriction of the airways;
- swollen throat or sensation of a lump in the throat that makes it difficult to breathe;
- shock with a severe drop in blood pressure;
- rapid pulse;
- dizziness, lightheadedness, or loss of consciousness.
What to do in case of a food allergy
The first thing to do if the signs and symptoms of food allergy occur is to consult your doctor to rule out other illnesses.
The family doctor can then refer you to a dietitian or an allergist.
In case the allergy affects children, the pediatrician should be consulted in any case to agree with him on the most effective prevention and treatment, but especially should be consulted in cases of hives, swelling, itching or other obvious symptoms of allergy about half an hour after ingestion of a particular food.
On the other hand, it is advisable to go to the emergency room immediately when the child has air hunger and coughs, resulting in a choking sensation.
Difference between food allergies and food intolerances
Food allergy is probably the most commonly self-diagnosed, but also often misdiagnosed condition by sufferers or parents (if it is a child), while it is not infrequently under-diagnosed by general practitioners and even specialists.
Especially at the diagnosis stage, it is important to distinguish food allergies from simple intolerances and aversions to certain foods.
True food allergies are characterized by an abnormal response of the immune system to one or more foods or food components.
Food intolerances are caused by the deficiency or absence of an enzyme (e.g., lactose intolerance is caused by reduced function of the enzyme betagalactosidase or lactase).
Food aversion is a psychological reaction caused by the association of negative emotions with certain foods.
Diagnosis of food allergy
A detailed history of the patient and his or her family is the first step in making an accurate diagnosis if food allergy is suspected.
It is also important to go over the “history” of reactions he or she has had with different foods.
Next, the patient should undergo a complete physical examination.
The most widely used method of determining whether one has a food allergy is to undergo Prick tests and/or immunoassays of serum IgE levels with specific foods.
An even more reliable test, the oral provocation test (TPO), – which consists of administering the suspected food, – carries the risk of eliciting a severe allergic reaction, however, and must therefore be performed under the supervision of qualified medical personnel with emergency treatment readily available.
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