At the Excellence in Paediatrics Conference, Madrid, academics from the International Scientific Forum on Home Hygiene (IFH),  a not‐for profit, non‐governmental organization which works to develop and promote home hygiene practice based on sound scientific principles, call for a radical change in how we think about cleanliness and hygiene in the home. 

The report tackles the long-held 'Hygiene Hypothesis', which suggests that keeping our children 'too clean' may lead to an increase in allergies and a decreased immune system and instead suggests we change it to an 'Old Friends Hypothesis'. The report agrees that we need exposure to some types of microbes to regulate our immune system but challenges the idea that this must include the germs that cause infectious diseases - the notion that children who have fewer infections because of more hygienic homes are more likely to develop asthma and other allergies. 

The report reviewed evidence since the 'hygiene hypothesis' was first proposed a few decades ago. It set out to examine whether the modern-day approach to home and everyday life hygiene has any bearing on allergies such as hayfever, and chronic inflammatory diseases (CIDs) including type 1 diabetes, multiple sclerosis and inflammatory bowel disease, all of which have risen in recent years.

The researchers concluded that a range of measures introduced over the past 200 years, such as sanitation, cleaner food and water, and antibiotics, have reduced or altered exposure both to harmful germs and to the microbes that regulate our immune system. Together with other contributory factors such as genetics, the modern-day diet, pollution and stress, this is making us more susceptible to allergies and CIDs. 

 Researchers urge citizens and policy makers to recognize that while exposure to the 'right' kind of microbes is essential, we must continue to ensure that we keep the 'wrong' kind of microbes - the pathogens that can make us seriously ill - at bay. The ongoing burden of infectious diseases, the greater numbers of people more vulnerable to infection, the problem of antibiotic resistance and the lack of effective vaccines against many infectious diseases mean that infection prevention remains a high priority health issue. Hygiene has an increasingly important role to play, and the IFH report recognises that it must take a higher place on the health agenda. 

 "Allergies and chronic inflammatory diseases are serious health issues and simplistically talking about 'being too clean' as the cause is ill-advised, because it's diverting attention from finding the true, probably much more complex, causes - and finding solutions to the problem" said Dr. Rosalind Stanwell Smith, Honorary Senior Lecturer at the London School of Hygiene and Tropical Medicine, UK, and co-author of the report. Worrying about 'being too clean' could result in people needlessly exposing themselves and their children to pathogens that can make them ill, which would clearly be dangerous. 

Professor Sally Bloomfield, Chairman of the IFH, Honorary Professor at the London School of Hygiene and Tropical Medicine, UK, and co-author of the report, added, "The key here is that we need to stop talking about being 'too clean' and confusing cleanliness with hygiene. We need to help people to distinguish between letting children have contact with their environment and getting dirty while also protecting them, as far as possible, against potentially harmful microbes. For example, we should encourage children to play and interact freely with each other and their environment, but rigorously enforce the need for actions such as hand washing after visiting the toilet, before eating food, after farm visits and so on.

 Professor Rook of the Centre for Clinical Microbiology, University College London, UK, and co-author of the report, is proposing that new research fits better with the idea that the microbes we need exposure to are not infectious diseases, because these evolved relatively recently in our past.

He proposes that the organisms we require are those that we were exposed to during the stone age when our immune systems were evolving - environmental microbes, the microbes which made up our normal body flora in those times and also helminths (worms). He calls this refinement of the hygiene hypothesis the 'Old Friends' hypothesis. "It is becoming apparent that we need to find ways to re-introduce exposure to these 'old friends', in our fight to beat the increasing number of allergies and other chronic inflammatory diseases that are plaguing modern society. But this will take time and further research. 

If the "old friends" hypothesis is correct, it is unlikely that simply relaxing hygiene and cleanliness standards will help because it is quite probable that our modern urban homes no longer contain many of these types of microbes or other helpful exposures." 

 This is the basis of the modified approach to home hygiene developed by the IFH and known as "targeted hygiene". The principle of targeted hygiene is to get people to understand which are the key routes by which harmful microbes are transmitted in our homes and everyday life, and to use hygiene measures like hand washing at the appropriate time to stop germs from spreading.

 They say that by focusing our own and our children's hygiene habits in this way, it minimizes the risks of infection, whilst disturbing other microbes, naturally present elsewhere in our environment, to the least extent. The IFH recognises that to make a meaningful and impactful change, national and international health bodies, environmental agencies and policy makers need to work together and share responsibility for changing attitudes, understanding and behavior at all levels of society.