Hygiene obsession may impair skin's ability to stay healthy.

From the UK's Telegraph:

Children should be allowed to play in the dirt because being too clean can impair the skin’s ability to heal itself, new research suggests.

By Murray Wardrop

Published: 8:00AM GMT 23 Nov 2009

Scientists have discovered that bacteria on the surface of the skin play an important role in combating inflammation when we get hurt.
The bugs dampen down overactive immune responses, which can lead to rashes or cause cuts and bruises to become swollen and painful.
The findings support previous research which suggests that exposure to germs during early childhood can prime the immune system to prevent allergies.
The so-called “hygiene hypothesis” has previously been used to explain why increasing numbers of children suffer allergies such as eczema and hay fever in more developed countries.
Parenting groups yesterday welcomed the findings as “a vindication of common sense” and urged parents to allow their children greater freedom to play outdoors.
Experts at the University of California at San Diego made the discovery by studying mice and human cells cultured in their laboratory.
The team, led by dermatologist Professor Richard Gallo, found that common bacteria called staphylococci, can reduce inflammation after injury, when they are present on the skin's surface.
Prof Gallo said: “These germs are actually good for us.”
He said that his team identified for the first time ever a previously unknown mechanism by which a product of staphylococci prevents inflammation.
The effect occurs because of a molecule called staphylococcal lipoteichoic acid that acts on keratinocytes, the primary cell type found in the epidermis – or outer skin layer.
Prof Gallo, whose findings are published in Nature Medicine, added: "The exciting implication of the work is that it provides a molecular basis to understand the hygiene hypothesis and has uncovered elements of the wound repair response that were previously unknown.
"This may help us devise new therapeutic approaches for inflammatory skin diseases."
Parents Outloud, the pressure group, said the research provides scientific support for its campaign to prevent children being mollycoddled by health and safety regulations.
Its spokeswoman, Margaret Morrissey, said: “Parents have become so paranoid about their children playing outside and getting dirty that today’s youngsters are not enjoying a proper childhood.
“You cannot blame parents for this because they are constantly bombarded with advertising telling them they have to buy antibacterial products to keep their children clean and healthy.
“However, hopefully research like this will help parents realise that it’s natural and healthy for children to get outdoors and get mucky and that it doesn’t do their health any harm.”
Sue Palmer, children’s campaigner and author of the book Toxic Childhood, added: “Clearly parents need to make sure their children are hygienic, but wrapping them up in cotton wool and not allowing them exposure to germs is just as damaging.”
Up to four in 10 people in Britain suffer from allergies, research by the charity Allergy UK has found.
The number of children with food allergies has tripled in the past decade, with millions being diagnosed with severe immune system disorders, some of them potentially life-threatening.