While we are reminded every cold and flu season of the importance of washing our hands, new research supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) says ridding our skin of all bacteria – if that were even possible – is not necessarily a good thing.

The study showed that staphylococcus epidermidis, the most common bacteria cultured from human skin, is not only innocuous in the skin of healthy people, but it also helps us, triggering a pathway that prevents excessive inflammation after injury.

In the paper, published in the journal Nature Medicine, Richard L. Gallo, M.D., Ph.D., and colleagues at the University of California, San Diego, found for the first time a mechanism by which a product of the bacteria inhibits skin inflammation. Such inhibition is mediated by a molecule called staphylococcal lipoteichoic acid (LTA), which acts on keratinocytes – the primary cell type found on the epidermis. The researchers also found that activation of a protein called Toll-like receptor 3 (TLR3), which recognizes products released by damaged skin, plays a role in the subsequent induction of inflammation.

These new findings offer some insight into the so-called “hygiene hypothesis.” First introduced in the late 1980s, the hypothesis is based on observational data that many populations that live in cleaner environments seem to get certain inflammatory diseases and other related disorders more frequently. But there has not been a rational biochemical mechanism to explain how cleanliness could be harmful. Dr. Gallo’s discovery offers a potential explanation, defining a bacterial molecule, a receptor and a pathway by which the phenomenon may be working.

While the new research may help explain cleanliness' downside, it is not an excuse to abandon good hygiene habits, says Dr. Gallo. Certainly, there are infectious bacteria and viruses that have adapted to survive the body's normal defenses and can potentially make you sick.

He says these findings could potentially lead to the development of new therapies for inflammatory skin diseases or possibly cleansing agents that remove harmful viruses and bacteria from the skin without interfering with the helpful ones.

The mission of the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), a part of the U.S. Department of Health and Human Services’ National Institutes of Health, is to support research into the causes, treatment, and prevention of arthritis and musculoskeletal and skin diseases; the training of basic and clinical scientists to carry out this research; and the dissemination of information on research progress in these diseases. For more information about NIAMS, call the information clearinghouse at (301) 495-4484 or (877) 22-NIAMS (free call) or visit the NIAMS Web site at http://www.niams.nih.gov.

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Lai Y, Di Nardo A, Nakatsuji T, Leichtle A, Yang Y, Cogen A, Wu Z, Hooper L, Schmidt R, von Aulock S, Radek K, Huang C, Ryan A, Gallo R. Commensal bacteria regulate Toll-like receptor 3-dependent inflammation after skin injury. National Medicine. 2009 Dec;15(12):1377-82.