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Feature

The Hygiene Hypothesis

Does it explain increasing allergies? Posted on: 15 Apr 08

Summary

Why do some people have allergies and some not? And why has the prevalence of allergic disorders been increasing over the past century, especially in industrialised, developed countries?
The hygiene hypothesis tries to explain why some people have allergies and some do not, and why the prevalence of allergic disorders has been increasing over the past century, especially in industrialised, developed countries. It suggests that the modern obsession with cleanliness may be counterproductive; in childhood, at least, resulting in the immune system becoming too sensitive to infection. Our reliance on antibacterial products with new born babies, has been linked to asthma and other allergic diseases.
The Hygiene Hypothesis was first proposed by David P. Strachan in an article published in the BMJ, in 1989, it was developed to explain why children from larger families were more likely to suffer from hay fever and eczema, both allergic diseases, presumably because they were exposed to more infectious agents through their siblings, than single child families. The hygiene hypothesis has become an important theoretical framework for the study of allergic disordershas with immunologists and epidemiologists. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents. Modern hygienic practices and effective medical care have diminished or eliminated exposure to many microorganisms and parasites during development
However, University College London's Institute of Child Health believe there could be a more direct cause. They believe that excessive washing with harsh soaps and abrasive skin care products is being blamed for a rise in allergic diseases such as eczema by stripping away a protective layer of skin. This, they write in the journal Trends in Immunology, might make people more vulnerable to an allergic disease.
Researcher Professor Robin Callard said many strong soaps, exfoliant beauty products and biological washing powders were all potent enough to strip away the skin's protective outer layer.
The UCL team has also shown that if the outer protective layer of skin is stripped away - using something as simple as sellotape - allergy-causing particles are able to penetrate the skin.
They are then taken up by specialised cells called Langerhans cells, which are found in the epidermis. Which then move from the skin to the local lymph nodes of the immune system, and induce an allergic response.
UCL's Professor Callard said: "Despite its popularity over the past 20 years there is very little supporting evidence for the "hygiene hypothesis".
"In contrast, there is mounting evidence from both studies of rare genetic conditions and our lab work to support an important role for abnormalities in the outer protective layer of the skin in allowing allergic sensitization."
The National Eczema Society, said: "Patients with atopic eczema have especially sensitive skin, and because soap and biological detergents de-grease the skin, if you are genetically predisposed to eczema you would be well advised to avoid using such products and switch to less abrasive and more nourishing emollients." products such as olive oil soap (soap made entirely from olive oil) may be far better for our skin and reduce the chances of developing allergic diseases such as eczema.

More information http://en.wikipedia.org/wiki/Hygiene_hypothesis
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=416594
http://news.bbc.co.uk/1/hi/health/6748207.stm

Mike Wood

Last updated on: 27/08/2010 11:40:18

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