Bacteria, Dirt on Skin Help Prevent Inflammation


Let your kids get dirty: researchers report that a bacterial species commonly found on the skin, Staphylococci, can help prevent inflammation and thus inflammatory skin diseases. This finding comes from the School of Medicine at University of California, San Diego (UCSD).

The popular “hygiene hypothesis,” which was proposed in the late 1980s, suggests that children who are not exposed to infectious agents and microorganisms early in life have an increased susceptibility to certain diseases. In essence, these children have a “clean slate” in some respects, and when they are attacked by bacteria, viruses, and other disease-causing organisms, their bodies are not equipped to most effectively fight off the attackers.

The hypothesis was first developed to explain why children from large families, who had more opportunity to be exposed to many infectious agents, were less likely to develop allergies like eczema and hay fever than children who had less exposure. Experts also use the hygiene hypothesis to explain why there is a higher incidence of allergic disease among people living in industrialized countries.


In this new study, investigators studied mice and human cells and found that the harmless bacteria Staphylococci, commonly found on the skin and in dirt, blocked a critical step in a chain of events that lead to inflammation. To do this, it makes a molecule called lipoteichoic acid (LTA), which acts on the main cell types, called keratinocytes, which are found in the outer layer of the skin (epidermis). LTA stops the keratinocytes from initiating an aggressive inflammatory response to injuries.

The investigators also found that Toll-like receptor 3 (TLR3) activation is necessary for normal inflammation to occur after the skin is injured. Dr. Gallo noted that keratinocytes need TLR3 to initiate a normal inflammatory response to skin injury, and this response is kept at bay by staphylococcal LTA. Dr. Gallo believes this study is the first time this relationship between TLR3, skin epithelium, and staphylococci has been shown.

Richard L. Gallo, MD, PhD, professor of medicine and pediatrics, chief of UCSD’s Division of Dermatology and the Dermatology section of the Veterans Affairs San Diego Healthcare Systems, noted that “these germs are actually good for us.” He also pointed out that the results of this study provide “a molecular basis to understand the hygiene hypothesis and has uncovered elements of the wound repair response that were previously unknown.” These results could potentially lead to new treatment options for inflammatory skin diseases.

Some people have long insisted that we are over-sanitized, and that the obsession with killing bacteria with antibacterial soaps, wipes, and other products have contributed to children being more susceptible to allergies and disease. In 2002, for example, an article entitled “Eat Dirt: The Hygiene Hypothesis and Allergic Diseases” appeared in the prestigious New England Journal of Medicine and stated that one of the main reasons for the epidemic of autoimmune and allergic skin diseases could very likely be the overuse of sanitizing practices, especially among young children.

University of California, San Diego
Weiss ST. New England Journal of Medicine 2002 Sep 19; 347(12): 930-31