The Science of Scratching

In terms of evolution, reflexes like scratching an itch may not seem as important as developing an opposable thumb. But scientists are finding that the "itch" and its good buddy "the scratch" are more neurologically complex than previously thought. In a new study, dermatologist and researcher Dr. Gil Yosipovitch, of Wake Forest University Baptist Medical Center, used functional magnetic resonance imaging (fMRI) to examine why scratching an itch can feel so good. And why it can become a serious problem in some cases. He spoke to NEWSWEEK's Joan Raymond about pleasure, pain and those itches you can--and can't--scratch. Excerpts:

Of all the medical issues plaguing mankind, why study something as seemingly innocuous as the itch and the scratch?
Good question. But first, the itch and scratch aren't necessarily benign. There are the acute problems with itch that everyone experiences. Take the mosquito bite. You get bit, you scratch a couple of times and then you move on. But for many people itching is chronic and debilitating problem. There are about 30 million people with eczema and some patients literally scratch themselves raw. Liver and renal problems and some cancers like lymphoma and diseases like HIV can also cause severe itching. People are miserable. They can't sleep at night. Their quality of life can be destroyed. And they can get serious infections and scarring from scratching so much.

How much headway has science made regarding itching and scratching?
Not as much as we should. But what we do know is that the itch doesn't stand alone. Rather the itch involves not only the skin, but also the spinal cord and the brain. We used to think that the itch shared the same neurological pathway as pain. But now we know that the itch has its own neural road, if you will. There are actually some nerves in the spinal cord that are itch specific.

The scratch is even more complex, even though it's essentially a reflex action that is controlled by the spinal cord. You don't have to think about scratching. You just automatically do it. And, hopefully, you'll hit the right spot. But that seemingly simple act requires a lot of neurons whose job is to coordinate all the actions that are necessary to relieve the itch. But there is still a question as to what is the link between the pathway of the itch and that of the scratch reflex. We don't know that, yet. What we wanted to show is some scientific evidence that itch may be inhibited by scratching and why.

Your study looked at the brain's reaction to scratching. How was the study designed?
One of the big questions is why does scratching relieve an itch? So we wanted to see what brain areas are involved. We had 13 healthy adult men and women volunteers for our study. We used a fMRI to track blood flow and see what brain areas activated or became suppressed when these volunteers felt the sensation of a scratch.

It's important to note that this was passive scratching. And these patients did not experience an itch, which was somewhat limiting. All we did was take a small brush and scratched their lower legs for about 30 seconds about 5 times over the course of five minutes.

Were you surprised by the brain's reaction?
Absolutely. What we found was that activity in certain brain areas, such as the anterior cingulate cortex and posterior cingulate cortex, was reduced. The cingulate cortex areas are linked to a lot of different things. The anterior region is activated when people think of difficult experiences or when you remember an unpleasant sensation like burning your hand. The posterior area is associated with memory.

So for these two areas to show decreased activity with the scratch, lends credence to the conventional wisdom that scratching is actually pleasurable. It seems that the reflex of scratching suppresses the emotional components of the itch, the misery of it, and brings about its relief.

Were there brain areas that were made more active?
Yes. The secondary somatsensory cortex, which is associated with tactile stimulations, like touch and pain. And the prefrontal cortex, which is associated with executive functions, like defining goals as well as obsessive behaviors.

Now that we have a somewhat better understanding of the processes, we might be able to devise some better treatments that work directly on the brain (for those whose scratching has become debilitating).

Until we get there, can we all just continue to scratch away?
Animals scratch and humans scratch. It helps remove irritants. It's an evolutionary defense mechanism, a reflex. But scratching an itch, though pleasurable, can really damage the skin if you go overboard.

Is there an itch we can't scratch?
Actually, yes: Hives. Though there is a lot of histamine and swelling, you don't see patients scratching much. Although you would think they would be scratching like crazy. We don't know why they don't find relief from scratching.

Is there any reason why I'm feeling itchy after talking to you?
We're currently gathering data for why people feel itchy when they see someone scratching. So feeling itchy while talking about the problem doesn't seem all that far-fetched.