Last Saturday, I headed to Brighton Beach for my first beach day of the season (pictured above. Photo by Mike Wasilewski using instagr.am). Despite a few shards glass poking out of the sand and a handful of muscly men blasting Russian techno nearby (a two-foot-tall subwoofer at the beach? Really?), it was a great day complete with ocean swims, kite flying and hot dogs.  And, of course, bright hot sunshine.  On the way home, despite three applications of 30 SPF, I started to feel a familiar prickly discomfort spread across my back.  And by the time the F train dumped us back home in Park Slope, it became clear that I was in for a few days of painful sunburn.

So, what caused that stinging tenderness?

Today, researchers from King’s College London report in Science Translational Medicine that the answer is CXCL5, a molecule from the chemokine family that controls pain sensitivity to UVB exposure. UVB is the type of ultraviolet radiation that causes direct damage to the DNA in our skin cells, and is the main cause of sunburn.

In the experiment, the researchers exposed small patches of skin on healthy adults to UVB light.  A day or so later, as the burns peaked, they took a punch biopsy of the damaged area, which is essentially like taking a hole punch to the skin.  Next, they analyzed those little skin bits for hundreds of substances that are associated with pain. One in particular, CXCL5, was there in abundance. To dive deeper into the biology behind this increase in CXCL5, the team turned to a trusty animal model, the rat. Like humans, sunburned rats had heightened CXCL5 at the peak of their sunburns. Injecting CXCL5 in sunburn-free rats increased skin sensitivity, and neutralizing it with an antibody made the pain disappear.

Giving rats sunburns and then playing with their CXCL5 levels sounds great and all, but how does this potentially apply to us?  In the future, CXCL5-blocking drugs could alleviate sunburn pain (although that doesn’t mean you shouldn’t wear sunscreen!).  Sadly, that relief is far, far in the future, the way drug discovery typically goes.  So for now, I guess I’m sticking with aloe.

Here, lead researcher Stephen McMahon explains further (video courtesy of Science/AAAS):