A little dirt never hurt

The wisdom of modern parents' obsession with germs and hygiene has been called into question by new research from the School of Medicine at the University of California, San Diego, which found that being too clean can impair the skin's ability to heal. Researchers discovered that normal bacteria living on the skin trigger a pathway that helps prevent inflammation when we get hurt. This lends credence to the adage that the more germs a child is exposed to when young, the stronger his or her immune system in later life.

The research, published in the online edition of Nature Medicine, claims that common bacteria known as staphylococci, which cause inflammation under the skin, are "good bacteria" when on the surface, where they can reduce inflammation. The findings bear out the "hygiene hypothesis" first proposed in the 1980s, which suggests that early childhood exposure to bugs might prepare the immune system to prevent allergies. "Our research shows that removing resident bacteria has a negative impact and, importantly, it explains exactly why in the specific scenario of skin rashes after injury," says Richard Gallo, a professor of medicine and paediatrics at the University of California who conducted the new research.

Of course, no one is suggesting a return to the awful pre-penicillin days when deaths from bacterial infections were 20 times greater than today. But have we swung too far in the other direction? Is our obsession with a sterile environment weakening our children's immune systems and leaving them at greater risk of developing allergies? "Yes," says Gallo. "It does show a negative impact on the normal function of the immune system."

Margaret Morrissey of the lobby group Parents Out Loud (www.parentsoutloud.com) also believes that our risk-averse culture does not do children any favours. "I think we have to be very careful because parents are being indoctrinated into believing that every kind of dirt is bad for children," she says. "Kids have a natural immune system which has to develop. If we protect them from every scrap of dirt this will never happen, and they will face a lifetime of problems. I look at the new generation of disinfectant sprays that kill 99 per cent of germs and wonder whether they are really such a good idea."

Her views echo those of a growing number of parents and health professionals across the globe who argue that, especially in the developed world, the domestic environment in which children grow up is now too clean. The idea that a little dirt is beneficial for children is a counter-intuitive one, especially for parents who have spent countless hours sterilising their baby's bottles. But unlike newborns, whose immune systems are still undeveloped, older babies and toddlers are remarkably robust.

To understand why not all germs are bad, we need to get a handle on the hygiene hypothesis. Lindsey McManus, an education executive at Allergy UK (www.allergyuk.org), explains: "It's one of the key theories about why more people are developing allergies now. Unless we live in a developing country, our bodies are not exposed to the same amount and variety of bacteria, microbes and parasites they were 30 or 40 years ago. Our immune system was designed to deal with these foreign bodies, so we developed antibodies to fight, for example, parasitic infections."

McManus argues that our immune system is now under-employed, so it looks for new invaders to repel. That's why we react strongly to things that are quite harmless for most people, such as moulds in food or airborne allergens such as pollen. She cites research carried out after the fall of the Berlin Wall: "When the Wall first came down, the incidence of allergies in East Germany shot up. Allergies were hardly known before that, but suddenly people were more affluent and living in better conditions. Children didn't grow up on farms or play outside as much, getting dirt on their hands and knees, so the incidence of allergies went through the roof.'

The allergic reaction occurs when our immune system turns on inflammation - normally a response to infection - in inappropriate situations. This reaction, according to the hygiene hypothesis, is responsible for the recent increase in asthma and allergies, which are both associated with inflammation. But according to new research by a team from Northwestern University in Evanston, Illinois, chronic inflammation may also increase the risk of diabetes, stroke and heart disease. Researchers studied health surveys of 1,534 children from Cebu City in the Philippines, where western levels of sanitation are generally absent. When the study subjects reached 20 years old, the team tested their blood for C-reactive protein (CRP), a marker of chronic inflammation. They found that the more pathogens they had encountered before the age of two, the less CRP they had at age 20. For example, every childhood episode of diarrhoea cut the chance of higher CRP later by 11 per cent.

"This takes the hygiene hypothesis well beyond allergy," says Tom McDade, who led the research team. He believes that early exposure to germs could reduce chronic inflammation later in life, and therefore the risk of developing a host of serious conditions. McDade hopes that one day we may be able to expose babies safely to the protective elements of germs without infection-related risks. For now, he is taking a lower-tech approach: "If my two-year-old drops food on the floor, I just let him pick it up and eat it."

This makes McDade an unusual parent in an age when we seem ever-twitchier about letting children play freely. A report last year by Play England, part of the National Children's Bureau, found that half of all UK children have been stopped from climbing trees, 21 per cent have been banned from playing conkers and - remarkably - 17 per cent have been told they cannot take part in games like tag or chase.

"Children are being denied many of the freedoms that were taken for granted when we were children," says Adrian Voce, the director of Play England. He argues that it is becoming a social norm for younger children to be allowed out only when accompanied by an adult. "Logistically, that is very difficult for parents because of the time pressures on family life. If you don't want children to play out alone and have not got the time to take them out, they will spend more time on the computer," Voce says.

According to Play England, "risky play" is of great benefit to children, teaching them resilience and independence. Parental fears have bred a generation of "cotton wool kids", over-protected and given little opportunity to let their bodies or imaginations run wild. Sue Atkins, the author of Raising Happy Kids for Dummies, shares this opinion. "I do think some parents have let concerns over safety get in the way of their children's ability to play freely," she says. "The fact that so few kids get to play outside now is a real shame. It makes them fit and healthy, and boosts their imagination and creativity. Many kids have become extremely passive - they expect to be entertained and are watching TV or playing video games all the time, which makes them very insular and hyper."

Atkins, a parent coach and the founder of Positive Parents (www.positive-parents.com), advocates a healthy balance between protectiveness and trust, letting children play alone or with siblings in the garden or with friends in the park whenever possible. She argues that as well as boosting their fitness levels, independent play also hones social skills, as children learn to negotiate and navigate the choppy waters of group dynamics - something they cannot learn slumped at home alone in front of a TV or games console.

Also key, Atkins says, is the way we impart our values to children. "If you are over-protective you are teaching your kids that the world is not a safe place," she says. "Those children then grow up risk-averse - they don't want to try anything new in case they hurt themselves or make a mistake. "Find a balance between keeping them safe and letting them go," she says. "If they make a mistake when they're young, try not to overreact. Instead, ask them: 'What did you learn from that?' The answer is usually not to do it again, so they're learning to protect themselves from harm."

McManus also advocates a common-sense approach. "My advice to parents is just be sensible," she says. "Don't be paranoid about letting your kids play in the garden or getting a bit muddy or mucky. That won't do them any harm at all." Of course, we all want our children to be safe and well. It is natural, especially with a first child, to be overprotective. But wrapping them up in cotton wool won't help them in later life. A little managed risk and the odd grubby knee may be the best thing for them.