Love to scratch your back Here's why

An itch can be the most vexing when it occurs on your ankles or your back, also providing the greatest relief when the particular part is scratched, reveals a study pointing to specific nerve fibres.

The results of a study show that an itch was perceived most intensely at the ankle and back, while the perception of scratching relief was less pronounced on the forearm.

"We first evaluated whether itch intensity was perceived differently at three body sites, and then we investigated the potential correlation between the pleasurability and the itch relief induced by scratching," said Gil Yosipovitch, professor of dermatology at Wake Forest Baptist Medical Centre, who led the study.

While it is known that small nerve fibres are involved in unpleasant sensations such as itch and pain, Yosipovitch along with researchers now suspect that there are also specific nerve fibres involved in pleasure.

Yosipovitch and colleagues induced itch on the ankles, forearms and backs of participants with cowhage spicules, which are known to cause intense itching, the British Journal of Dermatology reported.

Itch intensity and scratching pleasurability were assessed every 30 seconds for a duration of five minutes using a Visual Analog Scale (VAS) to rate intensity - 0 for no itch, up to 10 for maximum unbearable itch, according to a university statement.

Their results show that an itch was perceived most intensely at the ankle and back, while the perception of itch and scratching relief were less pronounced on the forearm.

"Another major finding of the paper explains the pleasurability of scratching the ankle appears to be longer lived compared to the other two sites," said Yosipovitch.

"We see commonly involved areas such as the ankle and back in itchy patients with skin disorders caused by eczema or psoriasis," he added.

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