For some years now, increased rates of childhood asthma and
eczema have been observed and the finger of suspicion has pointed to a lack of
microbes in overly-clean homes. This idea is known as the hygiene hypothesis.
A recent report from the International Scientific Forum on Home
Hygiene has concluded that this hypothesis is not correct.
It seems that microbes - or rather a lack of them - may well
be implicated in the increase of allergies but it is not a reduced quantity of bacteria, viruses and
intestinal worms that seems to be the problem.
We all have a vast population of "friendly"
microbes that live on our skin and in our body cavities - nose, mouth, gut and
so on. The bacteria alone are said to outnumber our body cells by ten to one. Without
exposure to this vast array of microscopic life, we cannot be healthy. We know
this, in part, because mice brought up in a sterile environment reliably fail
to develop normal, healthy immune systems.
These "friendly" microbes stimulate the immune
system in many interesting ways. They train it in infancy and help to keep it
finely tuned throughout life.
There is a further range of microscopic life that lives in our
homes – on surfaces, on dust flakes and so on. Living alongside these familiar
life forms is normal and healthy. Of course there are also occasional pathogens
that can cause illness. But every day babies and toddlers get away with licking
floors and other household surfaces without picking up diseases.
The report concludes that the hygiene hypothesis should be
replaced by the "Old Friends" hypothesis. This states that allergies
are on the increase because the mix
of microbes on and around us bodies has changed. It is no longer the same rich
brew that co-habited with our ancestors and is no longer quite what the
developing immune system needs. Our
immune systems evolved alongside these old friends, developing complex and subtle symbiotic partnership.
My grandmother grew up in the country, playing on the dung
heaps in the yard, in a home that teemed with rural bacteria. When she had ear
infections, the treatment was to pour her own urine into her ear. As her young immune
system dealt with this environment, it learned to deal
with a mix of bacteria that had probably changed little through the millennia.
My grandchildren, growing up in an urban environment, have encountered
a different range of microbes. If you could analyse their microbe population it
would not be smaller, but would certainly be different to that of their great,
great grandmother. There will be an absence of some of the "old
friends" that evolved alongside their ancestors for millennia.
It is not just an absence of dung heaps that has caused
this change. It has become normal for children to have several courses of
antibiotics for chest or ear infections. This will have affected their blend of
gut bacteria. Hygienic caesarian birth probably has an effect and so might bottle-feeding
from a sterilised teat instead of a mother's microbe-rich breast. Factors like
this are probably far more significant than how often their parents clean the
bathroom.
You may say this is not a revolutionary change of
hypothesis, so does it matter? Should we worry about hygiene, and if so where
and when?
Well yes, food and kitchen hygiene are important if we want
to avoid food poisoning. Hand washing can reduce the number of “tummy bugs” and
colds we contract. If someone in the family has a compromised immune system,
then extra vigilance is needed. And if someone in the family is already
asthmatic, then reducing house dust exposure might be helpful.
But we still have a lot to learn about friendly bacteria and
intestinal parasites. We don’t know the identity of these old friends and
whether it would be helpful to hold a reunion or not. It is a branch of science
that is relatively new and is only just starting to yield interesting
information. It will be a while before it comes up with any practical
suggestions.
So if you were worried about your house being too clean,
then you can indulge in a bit of anxiety-free cleaning. And if you were worried
about a degree of household squalor, then worry no more. The friendly bacteria
will carry on doing what they do, and cleaning, or not cleaning will probably
have no effect whatsoever.
To read more, here is a link to Science Daily
