The sensation of feeling itchy is complex. Scientists have been researching just how complicated a simple itch is.
The sensation is partly an evolved behavior, partly genetic and is also nerve pathway generated. Chronic itching and scratching can be disabling and there are a number of conditions that possess this unfortunate symptom.
The more researchers know about the causes of itching, the closer they can come to finding ways to ease it.
According to the Society of Neuroscience, “Scientists believe the sensation of itch, known medically as pruritus, may have developed to protect us from potential hazards such as disease-carrying insects. Scratching allows us to flick away a mosquito or flea before it can bite and leave its toxins.” (1)
The stimulus to itch is then protective as it motivates one to look at the itchy area to see what may be causing the sensation.
Interestingly, we don’t even need to have an actual insect crawl on our skin. Just viewing photos of “itchy” things such as bedbugs or skin rashes can make our skin feel the sensation of itchiness.
Scientist also have found that itching and pain share some of the same nerve receptors but send their messages via different circuits. The discovery of the “itch” gene is what clued researchers to realize that itching and pain are distinct sensations.
The “itch gene” is called Gastrin-Releasing Peptide Receptor (GRPR). It was discovered by Zhou-Chen Ph.D. and his team from Washington University School of Medicine, St. Louis. They found that mice bred to not have the GRPR gene did not scratch themselves as much as regular mice when injected with a pain medication that also stimulated scratching.
Conversely, when they gave mice that had the gene a chemical that blocked their GRPR, they did not scratch as much as when they were given the original painkiller. This led to the realization that pain is not controlled by the amount of GRPR while itching is affected by its presence or lack of it. (1)(2)
Chen says, "Many genes have been identified in the pain pathway. But itch research has lived in the shadow of pain research, and no one knew which gene was responsible for itching in the brain or in the spinal cord until now." (2)
Itching is also controlled by two different nerve pathways. The first is triggered by histamine, the chemical released in our blood when our bodies are exposed to an allergen such as poison ivy. The second is not histamine stimulated.
Researchers performed a study using a tropical herb called cowhage to explore itching not stimulated by histamine. “Cowhage induced a more intense itch sensation compared to histamine. Cowhage was the dominant factor in itch perception when both pathways were stimulated in the same time.” (3)
Awareness of these two pathways explains why anti-histamines sometime do not relieve a person’s itching.
All this research on itching is important as millions of people suffer from conditions such as liver disease, psoriasis or renal failure that cause them to experience uncontrollable itching. Some medications such as morphine can also cause itching as a side effect, which can be extremely distressing.
The hope is that new treatments and medication can be developed to block the itching response when needed.
sources:
1. Society for Neuroscience - Itch: More Than Skin Deep. Society for Neuroscience. Web. 10 Sept. 2011.
http://www.sfn.org/index.aspx?pagename=brainBriefings_10_itch
2. "Itch Gene Found - Could Lead To New Treatments That Target Itching." Medical News Today: Health News. Web. 10 Sept. 2011. http://www.medicalnewstoday.com/articles/78127.php
3. Papoiu AD. et al, “Cowhage-induced itch as an experimental model for pruritus. A comparative study with histamine-induced itch”. PLoS One. 2011 Mar 14;6(3):e17786.
http://www.ncbi.nlm.nih.gov/pubmed/21423808
Michele is an R.N. freelance writer with a special interest in woman’s healthcare and quality of care issues. Other articles by Michele are at www.helium.com/users/487540/show_articles
Edited by Jody Smith