Rising allergies are not caused by clean homes or overdoing hygiene, says new report

A new in-depth report published today concludes there is no justification for the idea that current standards of home cleaning and home hygiene are a factor in the rise in allergies.

The report represents the first detailed review by infectious disease and hygiene specialists of the ‘hygiene hypothesis’ – the idea that having fewer childhood infections, because of cleaner homes and smaller families, may be responsible for more children developing allergies and asthma.

The report finds that there is significant evidence that changing exposure to microbes1 may indeed be a factor in the rise in allergies. But it finds no evidence that cleaning habits prevalent today are to blame and it firmly dispels the notion that we are living in super-clean, germ-free homes.

‘The hygiene hypothesis and its implications for hygiene’ compiled for the International Scientific Forum on Home Hygiene (IFH)2, evaluates the various medical, public health, and environmental and lifestyle changes that might have altered our exposure to microbes, and outlines the various other theories put forward to explain the rise in allergies. It has been produced by Dr. Ros Stanwell-Smith3 and Professor Sally Bloomfield4, Honorary Professor at the London School of Hygiene and Tropical Medicine’s Hygiene Centre.

Britain is at the top of the asthma league and some estimates suggest that by 2015 half the European population will suffer some kind of allergy, But if microbial exposure is important, the critical changes remain elusive. A wide range of factors may have altered patterns of exposure to microbes, including measures introduced to protect health, such as clean water and food, sanitation, antibiotics and vaccines, as well as incidental factors such as the move from farm to urban living.

Reducing infectious disease has been a central focus of public health policy for over a century, but the Hygiene Hypothesis suggested there may be a price to pay in terms of increasing allergy. The report finds little to support this worrying idea.

‘We don’t have to get infected to be protected against allergies’, says public health expert Dr Ros Stanwell-Smith. ‘It’s looking more and more likely that exposure to the harmless microbes that live all around us, or to harmless doses of harmful ones, is what’s important’. A study of 24,000 Danish families published in the last few weeks comes to similar conclusions (British Medical Journal, 30 April 2004).

Far from being sterile, the report also shows that most homes abound with a rich mix of microbes – some harmless, others less so – however clean they look. ‘Our routine daily or weekly cleaning habits actually have little effect in reducing our “background” exposure to microbes’, says hygiene expert Professor Sally Bloomfield, ‘but what concerns me is that while our homes may look spotless, our hygiene standards in terms of controlling hazardous microbes aren’t as good as we think’.

At a time when more people than ever are reporting a bout of gastro-intestinal disease5, the report warns that the popular notion that we are becoming ‘too clean’ not only has the potential to further undermine defences against infection in the home, it may also jeopardise attempts to improve hygiene standards in hospitals, schools and restaurants.

While strongly supporting further research into links between microbial exposure and allergies, the report advocates renaming the ‘hygiene hypothesis’ the ‘microbial exposure hypothesis’ which better reflects current thinking. Allergists and immunologists are starting to say the same. ‘We need a name that is less likely to mislead people into feeling poor hygiene is OK’, says Ros Stanwell-Smith.

On the positive side, the report shows that it is entirely possible to improve hygiene standards and defences against infection without reducing ‘background’ exposure to microbes, should this prove to be in some way beneficial. As Sally Bloomfield explains, ‘the “targeted hygiene” approach IFH has been developing over the last seven years argues that we should focus our hygiene effort on controlling microbes in the places and at the times that matter, simply to prevent exposure to doses that could make us ill’. The targeted hygiene approach is based on the same risk analysis system (HACCP) that the Chief Medical Officer intends to introduce throughout the NHS to control hospital-acquired infections.