“Two-second rule!” our children shout as they snatch food off the floor and pop it into their mouths. It is oft stated that our lives and homes are too clean, that we need to get dirtier for the sake of our health. You have probably heard it referred to as the hygiene hypothesis. This concept, first introduced back in 1989, was quite specific, proposing that rising levels of allergies might be linked to lack of exposure to childhood infections, due to higher standards of hygiene. This hypothesis is now known to be incorrect.
Yes, microbes and our contact with them is vital to our health, but the devil is in the detail. It is now thought that during human evolution, microbes evolved an essential role in regulating our immune system. The most promising theories suggest that the microbes involved in this aren’t those that cause infections, but friendly microbes that make up our diverse human microbiome.
These are acquired by exposure to other people and animals, and from our natural environment. They ensure that our immune system doesn’t overreact to harmless stimuli like pollen, foods and our own tissues. Without them, we are at higher risk of developing allergies and immune disorders like type 2 diabetes or multiple sclerosis.
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A range of lifestyle changes including an increase in C-section births, less breastfeeding, smaller family sizes and less time outdoors are now seen as the likely causes of reduced exposure to friendly microbes, together with altered diet and antibiotic use, which adversely affect the composition of our microbiome.
But there is little evidence that personal or household cleanliness – as suggested by the hygiene hypothesis – is involved. The common childhood infections that hygiene measures are designed to combat appeared much too late in our evolutionary history to have evolved an essential role in the development of our immune system.
Despite this, a survey by the has found that the majority of news articles published over the past 20 years on the subject cite hygiene as a cause of reduced exposure to friendly microbes.
Clean up our act
Continuing to use this simplistic hygiene hypothesis misnomer to refer to the link between friendly microbes and our immune system is leading people to interpret this issue in a way that is quite wrong. And it is happening at a time when hygiene is becoming more important.  Our elderly population is growing, and immunity to infection decreases with age. Empowering us to practice good hygiene in order to take care of our own health, including reducing the need for antibiotic prescribing is now a part of the UK government’s health strategy and .
It may be helpful to encourage children to spend more time playing outdoors, or not to worry about picking up food from the floor unless there is good reason, but undefined , are unacceptable.
We are still a long way from knowing which beneficial microbes we need, and which lifestyle changes are most important to reconnect us with them. But we do know that hygiene in our homes and everyday lives plays a crucial role in preventing the spread of infectious diseases, which have a significant impact on health. It is not about obsessive cleanliness to create a germ-free home but targeted cleaning at times that matter. That is how we will break the chain of infection. Let’s clean up our act, and restore public confidence in hygiene.
