Researchers have discovered why scratching an itch may be so addictive. A team from Wake Forest University in North Carolina used imaging technology to follow the changes that take place in the brain when we scratch.
Activity was reduced in areas associated with unpleasant emotions, and memories, but increased in an area associated with compulsive behaviour.
The Journal of Investigative Dermatology study raises hopes of new treatments for itching disorders.
For some people the irritation of an itch can be so intense that they scratch so hard they draw blood.
Among those who are most badly affected are people with eczema and those on kidney dialysis.
The researchers used functoinal magnetic resonance imaging (MRI) technology to monitor the brains of 13 volunteers while they were scratched on the lower leg with a small brush.
The scratching went on for 30 seconds and was then stopped for 30 seconds - for a total of about five minutes.
The results showed reduced activity in an area of the brain called the anterior cingulate cortex, which is linked to unpleasant sensory experiences, and in the posterior cingulate cortex, which is associated with memory.
When the volunteers reported the scratching was most intense, activity in these areas was at its lowest.