Scientists study the factors that influence the pleasurability of scratching an itch

“The researchers measured itch intensity and the level of pleasure associated with scratching by using a visual analog scale and took ratings at 30-second intervals. They found that average itch intensity and pleasure were significantly higher at the back and at the ankle than on the forearm.”

As winter wears on, you might find yourself feeling increasingly uncomfortable in your rather dry skin. If, through itch-inducing negligence, you’ve forgotten to moisturize your skin on a regular basis, then you are probably fighting back the only way you know how: by scratching. Now, it does not take a scientist to figure out that scratching a bad itch can be incredibly satisfying and pleasurable. It does take a scientist, however, to figure out why and which areas are most pleasurable to scratch. An international collaboration of dermatologists have found that itch intensity and the pleasure associated with scratching varies according to the site of the itch.

The researchers, led by Dr. G.A. Bin Saif of the Wake Forest School of Medicine in North Carolina, obtained these results by evaluating the differences in itch perception at three different anatomical sites: the forearm, the ankle, and the back. They also looked at the level of pleasure derived from scratching at these sites in relation to the relief provided from scratching.

First, they induced “itchiness” in 18 healthy participants, 10 of whom were women, by rubbing cowhage spicules onto the designated site. Cowhage (Macuna pruriens) is an annual climbing legume found in the tropics. The pods of this plant are covered in spicules that cause an intense pruritus, itchy sensations, because of an active component they possess called mucunain. The investigators then scratched the sites with a cytology brush immediately after inducing the itch. The researchers measured itch intensity and the level of pleasure associated with scratching by using a visual analog scale and took ratings at 30-second intervals.

They found that average itch intensity and pleasure were significantly higher at the back and at the ankle than on the forearm. The pleasurability of scratching increased with itch intensity at the forearm and at the ankle, but this was not the case for the back. The back, however, proved to be the easiest site to relieve an itch.

Regardless of the location of the itch, relief due to scratching was most prominent when the itch intensity was at its highest, so the itchier the individuals were, the more relief they felt from scratching.

This in itself might not be very surprising to dry-skinned and itch-prone individuals, but you might be surprised to know that the pleasure the participants felt as a result of scratching their ankles remained elevated for a much longer period time during the act of scratching, despite a steady decrease in itch intensity over the same period of time. This was not the case for the back or the forearm.

The scientists were unable to explain why this might be so. Many factors can influence perceived itchiness, including nerve density, but this does not explain why the ankle was the most pleasurable area to scratch. The dermatologists hope to conduct further research on the differences between these sites and additional ones, such as the scalp, in order to understand these differences.

This study is relevant because researchers are trying to curb what they call the “itch scratch-cycle” that can exacerbate conditions such as atopic eczema. In addition, this is the first study that looked at differences in itch intensity at various sites. Unfortunately, it has become a standard procedure in the dermatological world to use the forearm as a model for itch induction.  This study indicates that this location might not always be an appropriate study site.

How can you apply these findings to your everyday life? Well, it all depends on what kind of sensations you are looking for. If you want quick itch relief, moisturize areas like your ankles and wrists regularly.  If, however, you’re looking for the slow burn and delight that comes from scratching a particularly strong itch, then disregard that last piece of unsolicited advice and scratch away!

Arielle blogs about science at www.salamanderhours.com

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