Scientists have long known that scratching causes a mild sensation(感知) of pain in your skin.2.　 Yet pain signals that travel to your brain relieve the itching only temporarily.The problem,says researcher Zhou-Feng Chen,is that when the brain receives those pain signals,it produces serotonin to help control the pain.When serotonin travels along the spinal cord(脊髓),it can“jump tracks,”moving from pain-sensing nerve cells to those that influence itch intensity.3. 

　　Although Chen conducted his study on mice,the same annoying cycle of itching and scratching is thought to occur in humans.4.　 Not exactly,says Chen.Serotonin is a neurotransmitter(神经传递介质).It is involved in growth,aging,and mood regulation.Blocking serotonin would have far-reaching effects throughout the body,Chen explains. 

　　The researchers are looking for other ways to break the cycle so they can help people with itchy conditions.One possibility:Affecting the communication between serotonin and the nerve cells that transmit the itchy sensation.5. 

　　A.Try to resist scratching it.

　　B.Until then,try not to scratch!

　　C.This pain masks the itchy feeling.

　　D.The result:The itch will be more and stronger.

　　E.So can blocking serotonin make you itch-free?

　　F.If the itch is really bothering you,talk to your doctor.

　　G.Scientists discover why scratching an itch can make it worse.

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