as hygienic as we are, we can never make
ourselves sterile. It’s not the number of
microorganisms, but the type.
Our skin microbiome needs a wide range of
species, but we can do very nicely without the
harmful ones. Due to various lifestyle changes,
we have gradually lost touch with our ‘old
friends’, the microbes that co-evolved with
humans and were present even in early hunter-
gatherers. These are the ones that help us toIs there such a thing as ‘too clean’?
Rates of allergies such as hay fever and asthma
have been increasing since the Industrial
Revolution. In 1989, epidemiologist Prof David
Strachan suggested a possible reason for this:
children were contracting fewer infections. He
proposed that infections at an early age equipped
the immune system to deal with allergens such
as pollen. So the general increase in cleanliness
deprived children of infections that protected
them against allergic diseases.
This idea, known as the hygiene hypothesis,
quickly took hold. “That gave rise to this idea that
we are too clean for our own good,” says Dr Sally
Bloomfield, honorary professor at the London
School of Hygiene and Tropical Medicine. It’s a
commonly mistaken view that growing up in our
ultra-sterile homes causes allergies.
To say that we’re currently too clean is an
oversimplification. “I think that’s a complete red
herring,” says Bloomfield. “We don’t need
exposure to harmful germs to prevent allergies;
we need exposure to beneficial germs.” Besides,“It’s perfectly fine for kids
to get muddy in the garden
- most of the microbes
found in garden soil will be
harmless anyway”
ABOVE Bacteria in the
human armpit SCIENCE PHOTO LIBRARYas hygienic as we are, we can never make
ourselves sterile. It’s not the number of
microorganisms, but the type.
Our skin microbiome needs a wide range of
species, but we can do very nicely without the
harmful ones. Due to various lifestyle changes,
we have gradually lost touch with our ‘old
friends’, the microbes that co-evolved with
humans and were present even in early hunter-
gatherers. These are the ones that help us toIs there such a thing as ‘too clean’?
Rates of allergies such as hay fever and asthma
have been increasing since the Industrial
Revolution. In 1989, epidemiologist Prof David
Strachan suggested a possible reason for this:
children were contracting fewer infections. He
proposed that infections at an early age equipped
the immune system to deal with allergens such
as pollen. So the general increase in cleanliness
deprived children of infections that protected
them against allergic diseases.
This idea, known as the hygiene hypothesis,
quickly took hold. “That gave rise to this idea that
we are too clean for our own good,” says Dr Sally
Bloomfield, honorary professor at the London
School of Hygiene and Tropical Medicine. It’s a
commonly mistaken view that growing up in our
ultra-sterile homes causes allergies.
To say that we’re currently too clean is an
oversimplification. “I think that’s a complete red
herring,” says Bloomfield. “We don’t need
exposure to harmful germs to prevent allergies;
we need exposure to beneficial germs.” Besides,
“It’s perfectly fine for kids
to get muddy in the garden
- most of the microbes
found in garden soil will be
harmless anyway”
ABOVEBacteria in the
human armpit SCIENCE PHOTO LIBRARY