Over the past few decades, allergies and asthma have become common childhood diseases, especially in developed countries. Almost 20 percent of Australians experience some kind of allergy, whether it's to food, pollen, dust, housemites, mould or animals.
When people suffer from food allergies, hay fever or asthma, their immune system incorrectly believes the trigger substances are harmful and mounts a defence.
The response can range from mild symptoms, such as sneezing and a blocked nose (in the case of hay fever), to anaphylaxis (from severe food allergies or bee stings) and asthma attacks.
We used to think the rise in allergic conditions was because we weren't exposed to as many early infections as previous generations. But the science suggests that's not the case.
However it seems being out in nature, and exposed to diverse (but not disease-causing) bacteria, fungi and other microorganisms may help protect against asthma and allergies.
Remind me, what's the hygiene hypothesis?
In 1989, researcher David Strachan examined allergy patterns in more than 17,000 children in England