Some of us enjoy a bath more than others, but personal preferences aside - are we too clean for our own good? This was the question debated last week at the Wellcome Trust in honour of its 'Dirt' Season.

Most medical students have heard of the ‘hygiene hypothesis’, whilst social commentators routinely bemoan our warped sense of perspective on ‘clean’ living.  But are there hard facts behind these stances, and what would be the consequences if we all got a bit more down and dirty?

Adam Fox took to the podium first and wowed everyone with his ‘Paediatric Allergist of the Year’ tagline. Until he explained that it’s one of the smallest fields in medicine, with only thirteen of his compatriots in the country. Nevertheless, he put forward some interesting allergy-centric arguments in favour of the motion. According to Dr Fox, hay fever was first described in the Lancet in 1819 - and it took the author (a sufferer himself) nine years to acquire twenty-eight cases. Fast-forward to 2011, and 40% of British children have an allergy. In fact, the UK leads the world in rates of allergic disease – just ahead of New Zealand and Australia. This can markedly affect quality of life – studies show that schoolchildren are 50% more likely to drop a grade from taking mock exams (in winter) to doing the real deal (in summer). But the rise in allergy can also have fatal consequences - Australia has reported a 350% increase in anaphylaxis presentations to A&E over past years. However, having convinced us of the rise in allergy, Dr Fox didn’t spend much time on possible causes (although this was billed as the focus of the debate). In his last slide he cited the ‘hygiene hypothesis’ as being likely, although he also said that low Vitamin D and paracetamol use were also possible contributors.

Next up was Graham Rook, eminent microbiologist. He made a more concerted attempt to answer the question in hand, explaining that the rise in allergy has coincided with a rise in chronic inflammatory disorders like multiple sclerosis and type 1 diabetes. These are all due to defective regulation of the immune system – but what is the cause of this? Rook reminded us that humans are in fact superorganisms that are less than 10% human. The bacteria in our gut consist of 10 times more bacteria cells than we have human cells, and 100 times more bacterial genes than we have human genes. These bacteria normally regulate the immune system, but something has gone wrong with them – and Rook thinks this is down to the great move of humans from farms into cities. He cited a fascinating study in support of this, where researchers allowed multiple sclerosis sufferers to develop worm infections, resulting in improvement of their disease. However, treating the worms when they got too much to handle then caused the disease to worsen again. Immune studies showed that regulatory mechanisms had been altered by the introduction of the worms, leading Rook to conclude that whatever it is that we’ve lost in modern-day cleanliness – the answer may lie in this type of research. Perhaps one day we might even be able to re-introduce the missing ‘dirt’ to our immune systems in the form of a pill or vaccine.

Arguing against the motion were Virginia Smith and Sally Bloomfield. Ms Smith gave a reading from her book ‘Clean: A history of personal hygiene and purity’ about attitudes and approaches to cleanliness through the centuries, but lost sight of the question at hand. Ms Bloomfield fared better, but shocked the crowd with her hard-line views (she is Chairman of the Scientific Advisory Board of the International Scientific Forum on Home Hygiene). She argued that the ‘hygiene hypothesis’ is simplistic, misleading, and has a detrimental impact on our attitudes to hygiene. This in turn is leading to the deadly rise of superbugs such as MRSA, whilst consumers now turn white at the thought of beansprouts for tea. Bloomfield takes issue with the idea that decreased microbe exposure is caused by a good hygiene. Au contraire, she says, modern homes are still infested with a rich mix of microbes – instead we should be blaming overuse of antibiotics and vaccines, water purification and food processing. She wants the ‘hygiene hypothesis’ to be renamed the ‘microbial exposure hypothesis’ - and she wants us to keep washing our hands.