U.S. researchers say bacteria that normally live on the skin actually help the body to heal itself by calming down overactive immune responses.

"These germs are actually good for us," said Richard L. Gallo of the University of California, San Diego School of Medicine.

The scientists found that a common — and usually harmless — strain of Staphylococci bacteria on the skin can help prevent excessive inflammation after an injury.

The research published online in Nature Medicine provides a possible mechanism for what is known as the hygiene hypothesis, the idea that a lack of exposure to germs in early childhood can affect the immune system.

The idea was first put forward in the late 1980s as a way to explain the lower incidence of allergies and immune diseases in large families and the higher incidence of such diseases in industrialized countries.

UCSD post-doctoral fellow Yu Ping Lai performed the experiments in mice and human cell cultures.

"The exciting implications of Dr. Lai's work is that it provides a molecular basis to understand the hygiene hypothesis and has uncovered elements of the wound repair response that were previously unknown," said Gallo.

"This may help us devise new therapeutic approaches for inflammatory skin diseases," he said.

Lai and her colleagues founds that the harmless Staphylococci bacteria produced a chemical called lipoteichoic acid, and this chemical stops cells on the outer layer of the skin from responding too aggressively to an injury.

Aggressive inflammation caused by the body's own immune system can sometimes impede normal healing.