New Clues About Why Sunburn Is So Painful

Researchers Put the Blame on a Protein That Triggers Pain When You're Overexposed to the Sun

By Jennifer Warner
WebMD Health News

Reviewed by Louise Chang, MD

July 6, 2011 -- It may come as cold comfort to those already suffering from the sting of a midsummer sunburn, but researchers have found a new clue that may help explain why sunburns are so painful.

Their study shows UVB irradiation targets a particular protein in the body called CXCL5 that plays a role in pain sensitivity. Overexposure to the sun causes the protein to be overexpressed and triggers the pain and inflammation associated with sunburn.

"These findings have shown for the first time the important role of this particular molecule in controlling pain from exposure to UVB irradiation," says researcher Steve McMahon, from the Wolfson Centre for Age-Related Diseases at King's College, in London, in a news release.

"But this study isn't just about sunburn -- we hope that we have identified a potential target which can be utilized to understand more about pain in other inflammatory conditions like arthritis and cystitis," says McMahon.

The Pain of Sunburn

In the study, researchers analyzed samples of sunburned skin from healthy people as well as rats and found more than 90 potential pain mediators that were stimulated in response to UV radiation.

They then looked at the biology behind these markers in rats to see which of the potential pain mediators was likely triggered by UV radiation.

The results pointed to CXCLS, which is part of a family of proteins known as chemokines that attract immune cells to damaged tissue, causing inflammation and pain.

Researchers found that CXCL5 was at its highest level at the time of maximum pain in the rats. In addition, injecting the protein into healthy rat skin caused hypersensitivity to pain.

Finally, researchers found treating rats with a neutralizing antibody that targets CXCL5 reduced the sensitivity to pain caused by UVB radiation.

They say the findings, published in Science Translational Medicine, may help identify CXCL5 as a potential target for new medicines to treat other painful inflammatory conditions.

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SOURCES: Dawes, J. Science Translational Medicine, July 6, 2011; online edition.News release, King's College. ©2011 WebMD, LLC. All Rights Reserved.

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