Arguably the most significant medical advance in history, in terms of lives saved, isn’t vaccines, or any particular treatment but simple hygiene. The recognition that unsanitary conditions lead to disease, the discovery that germs cause illness, and it’s corollary, that destroying germs prevents/cures illness. As a society we have become so conscious of cleanliness and sterile conditions that we buy antibacterial soaps by the gallon, demand antibiotics of our doctors and carefully regulate our children’s environments to remove any possible source of infection (ok not all of us but more than you might think). In the process are we compromising our overall health?

The “Hygiene hypothesis” has been put forward to explain apparent increases in the incidence of allergic diseases such as hay fever, eczema and asthma since industrialisation and in more developed countries. It essentially states that our immune system tuned to expect a certain immunological load from the environment in the form of infectious agents, symbiotic flora and parasites. If this load is decreased significantly through the use of antibiotics and cleaning agents then the immune system can cause problems such as over reacting to benign environmental stimuli (hay fever) or attack the body’s own tissues (autoimmune diseases such as Type 1 Diabetes). This hypothesis was given a boost in support this week with the publication of a study in mice that found exposure to common human intestinal bacteria provided a protective effect against developing Type 1 Diabetes.

It seems that you can have too much of a good thing, as in everything else optimal cleanliness is a matter of degree. Obviously I’m not advocating a return to the bad old days where raw sewage flowed in the street and we drew drinking water downstream from dead animals but we also don’t need to live in antiseptic bubbles. One of my favourite advertising campaigns is Persil’s “Dirt is Good” promotion for exactly this reason, I don’t even mind that they’re trying to sell me something on the back of it.