As our environment gets cleaner, our immune systems seem to be getting more disordered, leading some researchers to call into question the modern, Western obsession with hygiene. Eczema, asthma and hay fever, which used to be rare, are now more common, with asthma experienced by 20-30% of people in Australia and the UK. Genetics alone can’t explain such a steep rise in allergies, so why are the most hygienic and affluent societies seeing so many new cases of allergy? Could it be that we are cleaning ourselves sick?
Affluence and allergies- an upward trend:
Australia now has one of the highest rates of allergy in the world. Yes, we may be diagnosing allergies more freely now than in the past and previously unexplained symptoms are now known to be due to allergies, however, there appears to have been a real increase in allergies in the last 50-60 years. Allergy rates in West Germany in 1961 before the Berlin Wall divided the nation were equal to those in East Germany. Jump to 1989 and children born in West Germany are almost three times more likely to develop allergies than East Germany children. Curiously, the rates equal out soon after Germany was reunited bringing more wealth into the east. It seems something about the affluent lifestyle of the west made children more prone to developing allergies.
The hygiene hypothesis:
Because humans have always coexisted with viruses, bacteria and parasites, our immune system has evolved to deal with them. The immune system tolerates what is not harmful including new foods, pollens and otherwise harmless things. The onslaught of bacteria and viruses in infancy appears to switch on regulatory cells that can tell the difference between good and bad microorganisms. Deprived of an onslaught of bacteria and viruses in infancy, it is as though the body doesn’t make the immunoglobulin that it needs to distinguish harmless foreigners like food, dust and grass from harmful substances.
Here are some of the proposed ways we are losing our “old friends”:
- Cleaner water - means less exposure to parasites and water born infections.
- Modern living - its emphasis on refrigeration and fresh, as opposed to fermented, foods.
- Food technology and changes in diet (less fermented foods) have reduced our exposure to good bacteria, leaving us more open to allergies.
- Less exposure to dogs and farm animals means less parasitic infections and a higher allergy risk (allergic dermatitis in particular).
- Change in family size - As family sizes become smaller, reduced exposure to viral and bacterial infections before the age of 11 may be linked with higher hay fever rates.
How should we respond?
Let's face it, hygiene has saved the Western world from some of the more serious
infectious diseases present in the underdeveloped world, and what’s more the hygiene hypothesis is just that - a hypothesis. Reduced exposure to bacteria was happening much earlier than the 60's so there may be other factors involved. Children, who fight off an infection, may just have a stronger immune system to start with. Perhaps aberrant immune regulation is just as big a factor as genes and environment .
Other lifestyle factors like vitamin D deficiency and obesity may be driving this trend. Paradoxically, allergies are on the rise in some developing countries such as Nigeria, Gambia and Ethiopia, and to add to the confusion, asthma is not. Understanding of the distinct roles of the immune system, the environment, genes and how they affect target organs is needed before coming up with proven preventative measures.
Here’s the take home message:
You can’t control the water supply, farming techniques or housing but here’s what you can do:
- Let your children play outdoors,
- Encourage them to eat a natural diet, (legumes, beans, vegetables and fermented foods help build up good bacteria)
- Teach your children basic hygiene practices
- Finally, don't be too obsessed by cleanliness, dirt may not be as bad as you were taught.
References available upon request