A hygienic childhood does not harm a person's immune system, research suggests.
Parents have long been advised to "let their kids eat dirt", with the so-called hygiene hypothesis stating exposure to germs in the early years helps develop our immune systems – protecting against allergies, eczema and asthma.
These conditions are on the rise, with many pointing the finger at Western society's obsession with cleanliness.
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Writing in The Journal of Allergy and Clinical Immunology, scientists from University College London (UCL) highlight four factors that disprove this theory, arguing we cannot be "too clean for our own good".
"Exposure to microorganisms in early life is essential for the 'education' of the immune and metabolic systems," said lead author Professor Graham Rook.
"Organisms that populate our gut, skin and airways also play an important role in maintaining our health right into old age. So throughout life, we need exposure to these beneficial microorganisms, derived mostly from our mothers, other family members and the natural environment.
"For more than 20 years there has been a public narrative that hand and domestic hygiene practices, that are essential for stopping exposure to disease-causing pathogens, are also blocking exposure to the beneficial organisms.
"We set out to reconcile the apparent conflict between the need for cleaning and hygiene to keep us free of pathogens, and the need for microbial inputs to populate our guts and set up our immune and metabolic systems."
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After reviewing the available evidence, the scientists have argued the microorganisms that are typically found in a modern home – and could be cleaned away – are not needed for our immunity.
In July 2020, Danish scientists reported vaccines do not just protect against their "target infection", but also "enhance resistance" against "unrelated" pathogens.
Based on these results, the UCL team has argued we do not need to risk death by being exposed to potentially harmful microorganisms.
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Bugs that live in the natural environment are also increasingly being linked to improved health, with these being unaffected by cleaning or hygiene.
Finally, research suggests it may be the cleaning products themselves that trigger the damage that leads to allergies, rather than the removal of microorganisms.
"So cleaning the home is good, and personal cleanliness is good, but to prevent spread of infection it needs to be targeted to hands and surfaces most often involved in infection transmission", said Professor Rook.
"By targeting our cleaning practices, we also limit direct exposure of children to cleaning agents
"Exposure to our mothers, family members, the natural environment and vaccines can provide all the microbial inputs that we need".
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