A recent study on pain sensation opines that a certain set of nerve fibers may be responsible for making injured areas overly sensitive to touch. Results of the study were arrived at by studying such reactions in mice.

When a person has any kind of injury - a broken shin, for example a sunburn - the pain system becomes hypersensitive, firing up in response to normally painless sensations induced by, for instance, walking or a gentle massage.

While normally, this tenderness protects the vulnerable tissue as it heals, occasionally, the pain can overstay becoming chronic in conditions such as arthritis.

Now, neuroscientists Robert Edwards and Allan Basbaum from the University of California, San Francisco, and their colleagues have found that a small subset of nerve fibers could be routing innocuous touch sensations to a once-mysterious neural pathway when there's an injury.

"Surprise would be an understatement. No one knew anything about what these fibers were doing," Nature quoted Basbaum as saying.

The researchers found that the fibers, called unmyelinated low-threshold mechanoreceptors (C-LTMRs), are easily stimulated, unlike classic pain fibers, which respond only when the sensation is intense.

But C-LTMRs aren't usually used to detect light touch - this falls to another major group of sensory neurons - so their role was unclear.

The researchers then discovered that these fibers express VGLUT3, a protein necessary for the cells to send signals to other neurons.