The study led by University of California - San Francisco researchers found that healing was brought about by the anti-inflammatory effects of glucocorticoids - steroid hormones - produced by the adrenal glands in response to stress.
"Under chronic stress, these same naturally-occurring steroids damage the protective functions of normal skin and inhibit wound healing, but during shorter intervals of stress, they are beneficial for inflammatory disorders and acute injury in both mice and humans," said senior investigator Peter Elias, a UCSF professor of dermatology based at the San Francisco VA Medical Center (SFVAMC).
"We believe that our findings explain why this otherwise harmful component of the stress response has been preserved during human evolution," he said.
The scientists studied mouse models of three types of common skin irritations: irritant contact dermatitis, caused by exposure to an irritant such as a soap or solvent; acute allergic contact dermatitis, of the sort caused by poison ivy or poison oak; and atopic dermatitis, or eczema.
After exposure to irritants on a small patch of skin on one ear, one group of mice was returned to its regular cages, while another group was put in a stressful situation - being placed in very small enclosures for 18 hours a day over the course of four days.
The researchers found that the stressed mice showed significantly reduced inflammation and faster healing in all three types of skin irritation.
When stressed mice were simultaneously given mifepristone, which blocks steroid action, all of the healing benefits of stress disappeared.
"This demonstrated the central role of internal steroids in providing these benefits," said Elias.
According to Elias, the study provides a clue to an evolutionary puzzle: why, over millions of years, humans have preserved the tendency to produce steroids under stress.
"Our ancestors did not have an arsenal of pharmaceutical steroids available to treat acute illnesses or injuries," Elias said.
"This safe, effective internal anti-inflammatory system provides just the correct amount of steroids to promote healing, over a time interval that is too short to cause harm," he said.
The study appears in the Journal of Investigative Dermatology.