Australia and New Zealand have some of the highest rates of allergies in the developed world. Recent increases in the incidence of allergies over the last 25 years may be described as an “epidemic”. It is due to this increase that allergy is now classified as a major public health problem in the developed world.
One theory for the significant increase in allergies in recent years is known as the hygiene hypothesis. This theory states that the excessive cleanliness of modern living interrupts the normal development of the human immune system, which in turn leads to an increase in allergies. The link between cleanliness and allergies was first reported by David Strachan in 1989. During his studies of thousands of British children, he found that the incidence of hayfever was inversely proportional to the number of children in the household. It is thought that our developed lifestyles have eliminated the natural variation in the types and quantity of germs we come into contact with. These germs are needed for our bodies to develop a better regulated, less allergic immune system. In developing countries, where allergy rates are lower, children often grow up in rural homes, as part of a large family. They tend to come into contact with livestock and have poor sanitation, which increases the type and quantity of germs they are exposed to. These factors, coupled with low use of antibiotics, leads to less allergies. In westernised countries, children often grow up in urban homes, as part of small families with one or no siblings. Good sanitation, coupled with high rates of antibiotic use lead to an increased incidence of allergic disorders, such as hayfever.
Contrary to popular belief, children growing up in urban areas who attend childcare centres may benefit from being exposed to other children’s germs. Most parents will tell you that their young children in day care are constantly sick with a cold, cough or runny nose, especially in the beginning. This is because the childcare environment mimics a household with several children, where exposure to germs and cross infections is common. Despite the possible discomfort caused by recurring cold symptoms, according to the hygiene hypothesis, day care centres may be a healthy way to promote the natural development of a child’s immune system.
For more information, ASCIA website.
Reference: 1. The Five “D’s” of food allergy. Murdoch Children’s Research Institute https://www.mcri.edu.au/news/investigating-allergies-food-allergy-capital (accessed 6 March 2018)