Allergies are common - affecting as much as 30 percent of the population in North America. If you are lucky enough not to have allergies yourself, it's unlikely you don't know someone affected by this increasingly prevalent phenomenon.
Despite their prevalence, allergies are strongly misunderstood. There are many different things which may trigger allergic reactions, and many different ways allergies may show themselves. That said, many symptoms are inappropriately blamed on allergies. It is important to understand the difference. People with a lactose intolerance, for example, often believe they have a milk allergy. (Lactose is a sugar found in milk.) The inability to digest milk sugars, however, is not at all related to the much more serious milk protein allergy.
What are allergies, any way?
Medical professionals define an allergy as an immune-mediated, hypersensitivity reaction. Its when your immune system mediates a physical reaction to a substance that causes no symptoms in most people. (Non-immune reactions, such as food intolerances, are not allergies.
With food allergies, there is always the potential for severe or life-threatening reactions, which is not the case with other forms of food intolerance.
Although life-threatening reactions may not be as common with environmental allergies, they can trigger severe asthma attacks or debilitating nasal and eye symptoms in allergic people. Some non-allergic triggers, such as viral infections and tobacco smoke, can also induce severe respiratory symptoms in patients with asthma or other chronic lung diseases.
Tendency To Develop Allergies
The tendency to develop allergies runs strongly in families, although the specific allergies themselves are not inherited. For example, we commonly see children with peanut allergies whose parents have had asthma or allergic rhinitis. These conditions are obviously triggered by very different allergens.
If one parent is an allergic person, their child has about a 30 per cent chance of developing allergies. If both parents are allergic, this risk may approach 80 per cent.
Difficult To Predict & Prevent
While we are very good at diagnosing and managing allergies, we are not very good at predicting allergies and we are terrible at preventing allergies.
In the past, we hoped to decrease allergic sensitization through various dietary and environmental manipulations during pregnancy and early childhood. For the most part, however, these attempts have failed to impact long-term outcomes, and are no longer widely recommended.
Currently, the only universal recommendations we make for families at increased risk is to avoid environmental tobacco smoke, and to breastfeed infants for four to six months. All other attempted interventions have proven ineffective.
Different allergic disorders
There are a number of different allergic disorders, all of which fall under the same broad category referred to as atopy. These include asthma, allergic rhinitis, atopic eczema, and food allergies, along with other, less common atopic phenomena.
Anaphylaxis - A Dangerous Allergic Reaction
A severe, acute, body-wide and often life-threatening reaction to an allergen is known as anaphylaxis. It is most commonly seen with food allergies, drug allergies, or allergies to stinging insects.
Fortunately, fatal anaphylaxis is not overly common, with perhaps 10 fatalities per year in Canada from food and insect allergies.
Allergies On The March
Allergies have been increasing over the past 50 years. While there are a number of possible contributing factors, the precise cause of this epidemic remains unclear.
Some current estimates:
- As many as 10 to 15 per cent of children are affected with asthma.
- As many as five to 10 per cent are affected with atopic eczema.
- As many as two to four per cent of children are affected with food allergies.
- As many as 20 to 30 per cent of the general population has allergic rhinitis or hayfever.
The 'allergic march' refers to the well-recognized progression from allergic eczema and/or food allergies in infancy, to allergic asthma in toddlers and allergic rhinitis by school-age in many affected children.
Although almost any foreign protein has the potential to induce an allergic response in a susceptible person, there are a relatively small number of common allergens responsible for the overwhelming majority of allergic reactions.
Among patients with food allergies, nine foods are responsible for about 90 per cent of allergic reactions: egg, milk, wheat and soy are the most common in infancy, and peanuts, tree nuts, fish, shellfish and sesame seeds are most troublesome for older children and adults.
We currently estimate that one to two per cent of the population is allergic to peanuts, with a similar number of adults allergic to shellfish.
People with food allergies must strictly avoid the foods they are allergic to. Fortunately, the majority of children will outgrow allergies to eggs, milk, wheat, and soy. While only 20 per cent of peanut-allergic children appear to develop tolerance over time, this still offers some hope for affected families.
It seems that 85 to 90 per cent of children with food allergies will be allergic to one food only. Being allergic to more than three foods is relatively rare.
There are tremendous regional differences in Canada in the rates of sensitization when it comes to environmental allergens:
- While allergies to house dust mites are very common in warm, humid environments, such as southern Ontario and British Columbia, dust mite levels are very low across the arid prairies. Dust mite allergies are, therefore, fairly uncommon in the prairies.
- Ragweed is an enormously problematic allergen in central and eastern Canada, but not a concern west of Ontario.
- Outdoor mold spores are significant allergens across the prairies, but much less so on the coasts.
Sensitization to cat allergens is strongly associated with asthma across Canada, while dog allergens seem to be less of a problem overall. Patients with allergies to horses commonly report very severe symptoms with exposures, more so than with other allergens, for unclear reasons.
The symptoms of an allergic reaction vary substantially from person to person, and depend on a great number of factors.
Food Allergy Symptoms
Food allergies are usually easy to identify. Symptoms consistently develop within minutes to one hour after exposure:
- Trouble breathing.
As many as 35 per cent of infants with moderate-to-severe allergic
eczema may have an underlying dietary trigger. Some of these can be more
difficult to identify in this age group. In older children, the trigger
is usually obvious, and easily confirmed by an allergist.
Environmental Allergy Symptoms
Environmental allergies commonly trigger nasal or eye symptoms:
- Sneezing fits.
- Profuse nasal discharge.
- Itchy, watery or red eyes.
In patients with asthma, exposure to known allergens may trigger:
- Coughing fits.
- Shortness of breath.
environmental allergies may also be more subtle, with chronic exposure
inducing low-level airway inflammation that is not as obvious. This may
- A tendency to long-lasting colds.
- Recurrent ear or sinus infections.
- 'Twitchy' airways.
or wheezing easily with viral infections or after vigorous activities.
Children with asthma often cough without wheezing, and any child who
coughs frequently at night, with physical activity, or after laughing
and crying should be assessed with this in mind. Coughing to the point
of gagging or vomiting is a classic sign of childhood asthma.
the diagnosis of an allergy is relatively easy. You or your child can
be referred by your family doctor or pediatrician to an accredited
allergist, who is trained in diagnosing and managing allergic
After taking a detailed
personal, family and environmental history, your allergist may decide to
perform skin and/or blood testing to confirm or refute suspected
The testing is
fairly accurate when performed and interpreted appropriately.
Unfortunately, the testing can be misleading in some cases. Testing for
food allergies in the absence of a supportive clinical history, for
example, is associated with a high rate of false positive results and
may lead to inappropriate dietary restrictions.
the 'gold standard' for any allergy diagnosis is a controlled
challenge, although this may not be feasible or safe, depending on the
allergen in question and the severity of symptoms with exposure.
an allergy is confirmed, the first step in management is always
avoidance. While this is absolutely essential with food allergies, it
may not always be possible or practical for environmental allergens.
are many effective strategies for decreasing exposure to house dust
mites and their allergens, and it is possible to decrease exposure to
indoor furred animal allergens - usually by relocating the pet.
is extremely difficult to decrease exposure to outdoor seasonal
allergens, and there will still be other sources of environmental
allergen exposures at work or school, and at the homes of friends and
Once the environment is
optimized as much as possible, the focus changes to preventing
allergen-induced inflammation and other symptoms - acute and chronic.
we have a broad range of safe, effective treatment options for children
and adults with allergies. Most patients can be treated safely and
successfully, so if you or anyone in your family continue to be bothered
by allergies, please see your doctor.
Carr is Assistant Clinical Professor and Director of the Division of
Clinical Immunology and Allergy, Dept. of Pediatrics, University of
Published in Best Wishes, March 2007.