Cleanliness may increase risk of infection

Scientists in the US discovered that bacteria on the surface of the skin play an active role in combating inflammation.

The bugs dampen down over-active immune responses which can lead to rashes or cause cuts and bruises to become swollen and painful.

The findings may provide a molecular basis for the “hygiene hypothesis”. First proposed in the 1980s, this suggests that early childhood exposure to bugs might “prime” the immune system to prevent allergies.

The theory was developed to explain why allergies such as hay fever and eczema are less common among children from large families with a greater risk of spreading infection. It was also used to explain the high rates of allergic diseases in “cleaner” industrialised countries.

But the same bugs do not trigger inflammation when present on the epidermis, or outer layer of skin. In fact, the new studies conducted on human cell cultures show they actually reduce skin inflammation.

A previously unknown mechanism was identified by which a product of staphylococci inhibits the inflammatory response. The effect occurs because of a molecule called staphylococcal lipoteichoic acid (LTA) that acts on keratinocytes, the primary cell type found in the epidermis.

“To our knowledge, these findings show for the first time that the skin epithelium requires TLR3 for normal inflammation after wounding, and that the microflora helps to modulate this response,” said Professor Richard Gallo, who led the research at the University of California at San Diego.

The research appears online today in the journal Nature Medicine.

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