My opinion: It sounds like there are too many reasons to count for why humans itch. I have my own input that involves psychology. Many psychologists cite gate-control theory when describing itches. The spinal cord may send itch messages through certain nerves, or the open gate, and it requires a level of itching to stop these signals to stop them, or close the gate. However, this theory is used more for pain than itching, and as the article reveals, pain may turn to itch. Not to mention, since some itches are severe, and many people feel compelled to scratch them to no end, itch may also turn to pain. Ultimately, there are many types of itches, but it may be most important to focus on the severe, chronic itches, since 10% of people suffer from them. Since itches often appear to be of little medical worry, however, I'm not sure people care to do the research, or that the necessary funds are granted toward this purpose. Maybe this is why the current treatments for itches are rather ineffective. Does our society not consider skin care important because it is largely for cosmetic purposes? Are other conditions that are only severe on occasion also ignored? Or is this topic too complex to delve into? Feel free to comment.
Why do we itch?
Kate Lunau on the latest research and the close connection between pain and itchMark Hoon, a scientist at the U.S. National Institutes of Health and author of one of two recent studies on this little-understood sensation.
What are some of the reasons we itch? “Oh my gosh, there are a million,” says Dr. Lisa Kellett, a dermatologist at the DLK on Avenue clinic in Toronto. Beyond the common ones—skin problems such as eczema or psoriasis, an allergic reaction to a bug bite, or contact dermatitis caused by poison oak or ivy—it could be a “neurologic issue,” she says, such as the phantom pain some patients feel after a limb is amputated. Liver disease, kidney failure and cancer cause itch, even when the skin appears normal. Stress and emotional upset will also bring it on; even talking about itch might lead to a bout of scratching.
About one in 10 people will, at some point, experience severe chronic itch. Right now, “the drugs are not very good,” says Diana Bautista, an itch and pain researcher at the University of California at Berkeley, and author of the other new study. “There’s no treatment, and certainly no cure.” Even in the case of mosquito bites, poison oak or ivy, “antihistamines are only partially effective,” she says. “For chronic itch, they do nothing whatsoever.” Certain pain medications (such as opioids) cause severe itch, so much so that patients would sometimes rather go off their meds. People would rather put up with pain than an itch, Kellett notes; most of us, at some point, have scratched an itch till it bleeds.
The relationship between itch and pain is a complicated one. “Some things that cause pain turn to itch,” Bautista says, and vice versa. “Pain can also override itch,” such as when we scratch or apply heat or cold to chase an itch away. “Things that are painful actually feel good under the conditions of itch,” she says. “It’s a big mystery.” The sensation of itch is followed by an urge to scratch; however, the sensation of pain is accompanied by the opposite urge, to withdraw.