What is allergy?


Mast cells in close up

Revised 4 April 2020


What causes allergy symptoms?

What happens during an allergic reaction?


Common allergy triggers

Allergies tend to run in families

Allergy is increasing
Allergy is more common now than in our parents' and grandparents' generation. A number of careful studies in Australia and abroad have shown that the frequency of hay fever, asthma, eczema and even food allergy appears to have doubled in the last 30 years. It is a true increase, and not just because doctors are better at diagnosing allergies. In the last 10 years, similar increases in food allergy have also been observed in Australia, the UK and USA, particularly in peanut allergy. The explanation for this increase also remains unexplained, but eczema and delayed introduction of common allergenic food in early childhood increases the risk of food allergy in early childhood. Regular topical exposure of food to the skin (eg. food preparation workers or those using goats milk soap) increases the risk of food allergy in adults.

Why is allergy increasing?


-Lower rates of breast-feeding.

-Exposure to air pollution particularly exposure to particulate matter from diesel fumes. All of these increase the risk of asthma.

-Exposure to cigarette smoke in pregnancy increases the risk of asthma in offspring.


-Low vitamin D levels, and many others

Unfortunately, there is no conclusive evidence at this time to easily explain the dramatic rise observed in recent generations

The Hygiene Hypothesis
Babies are born with an immune system which is inherently biased towards developing allergic-like reactions. These are called "type 2 response". A more balanced immune response is thought to require early exposure to infections. The first year of life appears to be the critical time in which this balance changes to a form of immunity that makes allergy less likely. Early exposure to infection is thought to "reset the balance" of the immune system by stimulating so-called "type 1 immune responses" instead. For example, allergic respiratory disease is less common in those growing up on farms with very close contact to farm animals. Recent studies have shown that multiple upper respiratory tract infections ("colds and flu's") in the first year of life may reduce the risk of developing asthma and hay fever by up to 50 %. There is also evidence that exposure to some gut bacteria may also play a role in modifying how the immune system develops in the first year of life, leading to trials of so-called “probiotics” in an attempt to reduce the risk, although results have been disappointing.

There is no convincing evidence that...

... food additives, preservatives, pesticides or vaccination contributes to a higher risk of allergy.


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