Although one study found 38 per cent of people think they have a food allergy, in fact only one to five per cent do, and allergists commonly report spending most of their consultations refuting firmly held beliefs that have no scientific foundation.
Theories about allergy – some from medical research and some from lifestyle ‘gurus’ – have led to conflicting information, making it hard to know what to believe. Because of this, Sense About Science worked with me and a number of allergists, immunologists, respiratory scientists and pharmacists to produce Making Sense of Allergies, a guide tackling the many myths and misconceptions about allergies.
One common myth – something that I work on – is the link between allergies and exposure to microbes. So here is a hygiene and allergy reality fact check. (If you are allergic to gluten – Mamamia’s quinoa recipe is a winner. Post continues after video.)
Do fewer childhood infections mean more allergies?
No. Although a link between allergies and microbes is largely accepted, the idea that more infections during childhood reduces the chance of developing allergies is now discounted. This idea came from the hygiene hypothesis, proposed in 1989, which theorised that the 20th century’s increase in allergies was due to lower rates of infection in early childhood. This hypothesis was based on observations that larger family size protected against hay fever, while smaller families were thought to provide insufficient infection exposure because of less person-to-person infection.
Exposure to a normal range of microbes during the first months after birth is critical to developing the immune system, but there is no evidence that “regular” infections are important to boost general infection immunity or prevent allergies.
Are allergies up because of modern obsessions with cleanliness?
No. Our microbiomes, the population of microbes that live in and on our bodies, have altered from previous generations. This is not because of cleanliness, but because we interact with less diverse microbial environments than those of our largely rural ancestors. The idea that excessive cleaning has created “sterile” homes is implausible: microbes are rapidly replaced by organisms shed from us, our pets, raw foods and dust.
This understanding has come from the “old friends” mechanism, a refinement to the hygiene hypothesis that offers a more plausible explanation for the link between microbial exposure and allergies. It proposes that exposure to the diverse range of largely non-harmful microbes or parasites that inhabit our world are important for building a diverse microbiome that is vital for sustaining a well regulated immune system that doesn’t overreact to allergens like pollen. These “old friends” have co-evolved with humans over millions of years. By contrast most infectious diseases only emerged over the last 10,000 years as we came to live in urban communities.
Old friend microbes are still there, but we have lost contact with them due to lifestyle and public health changes over the past two centuries. Improved water quality, sanitation and urban cleanliness have massively reduced infectious disease, but inadvertently deprived us of exposure to these microbes.
Changes in microbial content of food, less breastfeeding, more caesarean sections, urban rather than rural living and increased antibiotic use have also reduced early life old friends interaction. (Post continues after gallery.)