Author: Hoi See Tsao
Institution: Wellesley College
Date: June 2007
Most people have heard of one form or another of the "hygiene hypothesis," whereby the cause of allergies is linked to our high degree of cleanliness and our immune system's resulting oversensitivity to infection. However, researchers at University College London's Institute of Child Health have uncovered another piece of the allergy puzzle--the overuse of harsh soap and skin care products may be a more direct cause of allergic diseases such as eczema. According to research published in the journal Trends in Immunology, these products remove a protective layer of skin and increase people's vulnerability to allergic diseases.
Lead researcher Robin Callard explained to BBC.com that many strong soaps, exfoliating beauty products and biological washing powders are able to strip away the protective outer layer of the skin. His work demonstrates that this layer is particularly weakened in people with a rare genetic skin disease that causes them to develop allergic diseases such as eczema.
By stripping away the outer protective layer of skin, using methods such as adhesive tape to simulate the effects of harsh soaps, the team was able to support their hypothesis and show that allergens were able to penetrate the skin, where they were taken up by Langerhans cells. Langerhans cells are specialized cells found in the epidermis layer of the skin. An allergic response is induced when the Langerhans cells move from the skin to the lymph nodes in the body.
"Despite its popularity over the past 20 years there is very little supporting evidence for the hygiene hypothesis,'" Callard said. "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."
Researcher John Harper said that people should not be fearful of maintaining a normal level of hygiene. It only becomes problematic when people use harsh cleaning products excessively. "Good standards of hygiene are clearly important to prevent spreading of unpleasant diseases. But if this proposed mechanism does turn out to be true, we may be able to reduce the incidence of these diseases by developing new treatments which specifically target the outer protective layer of the skin," Harper said.
"Patients with atopic eczema [a form believed to be in part hereditary] have especially sensitive skin," said Margaret Cox of the National Eczema Society. "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."
Written by Hoi See Tsao