An allergy occurs when the body's immune system over-reacts to an otherwise harmless substance by mistakenly labelling it as a threat and triggering an immune response against it. These substances are termed allergens and may trigger symptoms through ingestion, inhalation or direct contact with the skin.
Allergens are therefore responsible for causing conditions such as contact dermatitis, allergic rhinitis, food allergy and anaphylaxis. They are also often a contributing factor to atopic conditions such as asthma, atopic dermatitis (eczema) and urticaria.
Allergy Facts and Statistics
Allergies are very common in Ireland. About 29% of Irish people suffer from some type of allergy and this is rising. These rates are similar to those found in other European countries.
Roughly 15% of the population have complex allergy problems requiring specialist care.
10% of children and young adults have more than one allergic disorder such as food allergy, eczema, asthma and nasal allergy.
IgE Mediated Food Allergy is found in 5% of young Irish children and about 2% of older children and adults. The majority of children who have food allergy also suffer from other allergic conditions such asthma, allergic rhinitis and especially eczema.
Food allergy typically results in symptoms such as rash, facial swelling or airway symptoms within 90 minutes. Deaths due to severe allergic reactions known as anaphylaxis are thankfully rare and are estimated to occur in 1 in 1-3 million people per year. These fatalities are more commonly triggered by medications, blood transfusions or insect stings rather than food allergy.
Food intolerance, as opposed to food allergy, typically result in symptoms such as bloating, flatulence, diarrhoea and abdominal pain. Food intolerances do not result in dangerous or life threatening allergy symptoms. There is no reliable method of testing for food intolerances and instead an exclusion diet followed by reintroduction is used.
Allergic Rhinitis / Hay Fever
Allergic Rhinitis (nasal/sinus allergy) is the most common allergic condition and affects about 26% of Irish people. The prevalence in Europe is estimated to vary between 17-29% and it is thought to affect at least 400 million people worldwide.
The prevalence of Allergic Rhinitis (nose/sinus allergies) is rising. The ISAAC study (2006) found an increase in the prevalence of Allergic Rhinitis from 13% to 19% during an 8 year period in 13 year olds. A smaller study in Cork demonstrated an increase in prevalence from 7.6% to 10.6% over a 5 year period in 6-9 year olds.
Allergic Conjunctivitis (eye allergy) is typically caused by airborne allergens such as pollen or house dust mite and is therefore also linked with nose and sinus allergy.
Asthma is a common chronic respiratory condition which affects 10% in Irish children and 7% of adults. The prevalence of asthma in Ireland is among the highest in the world.
Asthma is the most common chronic disease of both children and adults in Ireland.
In 2011, Asthma was responsible for 20,000 attendances at Irish hospital emergency departments.
The link between allergic rhinitis and asthma is well documented. Treatment of co-existing allergic rhinitis is recommended by the GINA guidelines to optimise asthma control.
Eczema (atopic dermatitis) is a common chronic inflammatory skin condition. Eczema affects 20% of Irish children and it is found in 3% of Irish adults.
Eczema classically occurs on the cheeks in early infancy at 3-4 months of age. The symptoms usually begin before the age of 2 and often first occur at around 3-6 months of age.
Eczema usually improves with age as the skin becomes thicker and more robust.
Exposure to irritants or the development of an allergy to an inhalant such as house dust mite, mould or pollen can lead to eczema relapse and exacerbation.
Urticaria / Hives
- What is an allergy?
An allergy occurs when the immune system overreacts to an otherwise harmless substance and generates an immune response against the perceived threat. This results in immune memory against that particular substance so that future exposure may cause a more aggressive reaction. The symptoms depend on the nature (inhaled, ingested, contact) and extent of the exposure. Once you develop sensitivity to an allergen, an allergic response is triggered every time you are re-exposed to it.
- What causes allergies?
While you do not inherit a particular allergy directly, you may inherit a tendency to be allergic. It is therefore very common for allergies to run in families.
After the initial exposure the immune system labels the substance as a threat by producing specific IgE antibodies against it. This primes the immune system to react more aggressively to any further exposures. When re-exposure to the allergen occurs, immune cells such as Basophils and Mast cells in particular are activated and release chemicals including histamine, leukotrienes, cytokines and prostaglandins. These chemicals cause allergy symptoms and further activate other immune cells.
- Why are allergies becoming more common?
The cause for the rising prevalence of allergies is not fully understood but it is known that certain risk factors make allergy more likely. These risk factors include overuse of antibiotics, exposure to air pollution, maternal/passive smoking and climatic factors.
Certainly, environmental exposures are key to understanding the rising prevalence of allergies. The ‘hygiene hypothesis’ was proposed as an explanation whereby the more sterile Western lifestyle was reducing parasitic infections and resulting in less type 1 immune responses. More recently, there is a better insight into the development of allergen tolerance with the microbiome during early life being an essential component. Antibiotic use will disrupt this amongst other environmental factors.
- Allergy symptoms
Allergy symptoms are dependent on the nature and degree of exposure to an allergen as well as the degree of immune system sensitisation.
IgE mediated Food Allergy symptoms can include rapid onset of a rash, facial swelling, airway symptoms and sometimes gastrointestinal symptoms such as nausea and vomiting. If these symptoms occur rapidly and quickly worsen then this is usually indicative of a severe reaction known as Anaphylaxis.
Hay fever (seasonal allergic rhinitis) primarily affects the eyes and nose but it may also exacerbate asthma and eczema. Symptoms of hay fever typically include sneezing, a runny or congested nose and watery, itchy eyes.
Eczema (atopic dermatitis) is characterised by itchy, red inflamed skin.
Contact Dermatitis is a type of dermatitis that is caused by the skin coming into direct contact with an allergen e.g. nickel. It is characterized by itchy red skin that occurs in the same distribution as where the allergen was in contact with the skin.
Asthma symptoms include cough, wheeze, breathlessness and chest tightness.
Urticarial hives appear like red (or pale) raised patches on the skin. They are typically itchy and can be aggravated by cold, heat, pressure, exercise and stress. Urticaria may occur in response to a wide range of potential triggers.
- What are the most common allergens?
Allergens can be foods, airborne particles or chemicals.
- The most common inhalant allergens are house dust mite, pollen (grass, tree and weed), animal dander, mould spores and feathers.
- The most common food allergens are egg, milk, nuts, fish and shellfish. In adults, new reactions to food are more likely to be food intolerances rather than an IgE mediated allergic reaction.
- Some insect bites and stings can also cause allergies.
Cigarette smoke and the chlorine found in swimming pools are sometimes considered a trigger of allergic symptoms but these are actually irritants rather than allergens. While irritants can cause symptoms which mimic allergy symptoms they can also aggravate an existing allergic condition such as hay fever, asthma, eczema or urticaria.
- Diagnosing allergies
There are three reliable methods of allergy testing available: Skin Prick Allergy Testing, RAST IgE specific blood testing and Patch Testing.
Skin Prick Allergy Testing and IgE specific blood testing can be used to detect allergies to a wide range of foods and airborne allergens. Skin prick allergy testing is the primary method used to test for allergies and as such this is the procedure used in Allergy Ireland and all major allergy centres. A pin is touched against the skin to introduce a drop of the suspected allergen. The size of the wheal and surrounding redness on the skin indicates how strongly you are allergic to a particular allergen. Skin prick testing results are available within 15 minutes. It is vital that the results are interpreted by a suitably qualified doctor.
Patch testing is used specifically to identify contact allergic triggers in a skin condition called contact dermatitis. The results must be interpreted by an Allergy Doctor or Dermatologist.
- Severe allergic reactions
Anaphylaxis is the medical term for a severe and possibly life threatening allergic reaction. It is most often triggered by the ingestion of a specific food or by medical administration of intravenous general anaesthetic or antibiotics. The symptoms typically occur within minutes of exposure and worsen rapidly. Urgent medical treatment is required.