Scratching an itch is likely to make it worse, according to a new study from the Washington University School of Medicine.
Itching causes the brain to releases serotonin, usually produced as a result of pain. The chemical increases itchy feelings, leading to a viscous cycle of itchy feelings and scratching.
Scratching skin creates a mild amount of pain, which can temporarily block signals carrying itchy feelings to the brain.
"The problem is that when the brain gets those pain signals, it responds by producing the neurotransmitter serotonin to help control that pain. But as serotonin spreads from the brain into the spinal cord, we found the chemical can 'jump the tracks,' moving from pain-sensing neurons to nerve cells that influence itch intensity," Zhou-Feng Chen, director of Washington University's Center for the Study of Itch, said.
Chen and his team carried out a study in mice, showing the relationship between scratching and itchy feelings, which they believe also take place in humans. Release of an itch receptor called GRPR, located in the spinal cord, is triggered by increased serotonin levels, increasing the flow of messenger chemicals to the brain, signaling feelings of itchiness.
Itching can be caused by movements of body hair or small particles of dust, as well as a variety of skin conditions.
Serotonin has been known for decades to play a vital role in the control of pain, but this is the first time the biochemical regulator has been shown to play a role in itchiness. Chen and his team found that reducing serotonin levels in mice greatly reduces itching. However, the chemical is vital to human physiology, and reducing serotonin in human bodies would likely cause significant, undesirable side effects. In addition to regulating mood, the chemical is essential to growth, aging, and metabolic actions within bones. Anti-depressants like Prozac act by increasing levels of serotonin in those people suffering from depression.
Mice were bred without the ability to manufacture serotonin. These creatures were then injected with a chemical that normally causes itching, with little effect. However, when serotonin was introduced to the bodies of the rodents, normal itching patterns developed in the test animals.
Researchers from the United States and China released a study in 2013 showing that chronic itching may be tied in with pain signals carried in nerves.
Even if serotonin levels can not be changed in humans without severe repercussions, it may be possible to develop a drug that would interfere with transmissions between the chemical and GRPR, in order to treat chronic itching.
Research into the act of itching, and the role of serotonin in response to the act, was detailed in the journal Neuron.