The Hygiene Hypothesis is a topic that may be of some concern to those of us who are responsible for keeping households clean. The general thinking that seems to be promoted by many doctors – and advertisers – is that you should wage a war on germs. Every item in your household should be germ-free, and you should do everything in your power to eliminate every possible germ in every possible hiding place. Even when you’re out and about, you should carry hand sanitiser and other odds and ends to keep yourself free from infection. And these safeguards should be doubled or even trebled if you have small children in your home to look after.
But according to the Hygiene Hypothesis, there is such a thing as being too clean. First proposed in 1989 by D.P. Strachan, this hypothesis suggests that children need to be exposed to a certain amount of bacteria at an early age so their immune systems don’t get a proper workout, so to speak, and so the immune system starts reacting to innocuous substances – which results in hay fever, eczema and other allergy-type problems.
The mechanism proposed for how the Hygiene Hypothesis works is as follows. Basically, everyone has several types of white blood cells (which are the blood cells responsible for fighting bacteria and viruses), two important ones being the TH1s and the TH2s. Too many TH2s cause allergic conditions. The Hygiene Hypothesis suggests that exposure to bacteria somehow regulates the production of TH2s, either by making sure that enough of another type of white blood cell, the regulatory T cells, or else by making sure that the body produces enough TH1s to balance the TH2s (not that TH1s never misbehave – they are responsible for Type 1 diabetes, MS and inflammatory bowel disease).
According to the Hygiene Hypothesis, it’s important that developing immune systems are exposed to mycobacteria and lactobacilli to prevent the imbalance of TH2 white blood cells. This has led to the practice, in some circles, of some children receiving special tablets containing these bacteria. However, this does have a faintly ridiculous ring to it – sterilizing the environment like anything to kill germs then carefully taking a pill to get enough germs to help your system!
Support for the Hygiene Hypothesis is fairly good – it is certainly true that allergies are more common in the developed world and smaller families (where big brothers and sisters don’t bring home colds from school to infect the younger ones), and urban families that don’t have contact with animals. Studies are still underway, and, like all scientific ideas, the Hygiene Hypothesis is still being debated to and fro. But on the whole, support for the idea is pretty good.
Some cynics might add that people in small urban families in the developed world are getting hay fever and eczema, but they aren’t getting tuberculosis, dysentery or cholera, and if you had a choice between which illnesses you’d prefer, most people would prefer to live with the allergy than put their lives at risks.
Of course, the Hygiene Hypothesis doesn’t mention some of the other side effects of keeping your home sterilised, such as exposure to antibacterial chemicals and the negative effects of stress caused by pressure to keep as clean as a hospital and constant worry about germs.
The answer for those of us who are actually responsible for house cleaning? Firstly, don’t panic. Yes, you should be sensible about keeping food clean and washing hands before meals, after going to the toilet and after playing with animals. Yes, you should keep food surfaces clean, and get rid of obvious dirt and unpleasantness around the house. Clean clothes, clean bodies and clean food are all still important. But don’t worry about keeping the toilet seat and floors so clean you could eat off them – you’re not going to eat off them, are you?! Let children play outside and get dirty occasionally – and maybe go and join them. It’ll be better for your stress levels, and that’s got to be good for you.