Itching happens in your brain, not on your skin, according to researchers at the University of Erlangen-Nürnberg in Germany.
There are at least two types of itch - one that is induced by immune-response chemicals called histamines, and another that is not.
Now, a new study suggests that the body, and possibly the brain, react differently to these two itches.
This is important because most itches do not respond to antihistamine medications, such as Benadryl.
For the study, a team including Clemens Forster, an itch and pain researcher at the University of Erlangen-Nürnberg in Germany, applied either histamine or extracts from cowhage - a tropical plant long used for studying non-histamine-induced itch - to the forearms of healthy volunteers.
The researchers then recorded the blood flow to the skin on the arm that had been given the itch stimulus.
Both itch inducers caused blood vessels in the skin to contract. However, the reaction was stronger in the case of cowhage, Forster said.
The volunteers rubbed with cowhage had lower blood flow to the skin, maintained for a longer period of time, compared with those rubbed with histamine.
The researchers also recorded how volunteers reported feeling the itch. Cowhage-triggered itching tended to be pricklier, sharper, and more stinging compared with histamine itch.
And scratching the cowhage itch didn't relieve the sufferers as much as scratching the histamine itch did.
Forster said that the exact neural mechanism behind the sensation is not yet known, but "Itch happens in your brain, not on your skin."
Neuroscientist Matthias Ringkamp of Johns Hopkins University School of Medicine in Baltimore, Maryland, said the finding that there is a distinct response to the two itch types suggests that the desire to scratch is induced through at least two types of peripheral nerve fibres and their associated pathways,.
"It's a great expansion on our own work," Nature quoted Ringkamp, as saying.
The study was reported on 17 November during the Society for Neuroscience's annual meeting in Washington DC.