Itching is an unpleasant sensation that everyone has experienced. Known as “itch” or medically as “pruritus,” it is a bodily reaction aimed at protecting us from parasites and irritating substances. While many people consider itching to be merely annoying, it plays a significant role in our immune system. In this article, we will explore the causes and mechanisms of itching and provide tips on how to deal with it.
What is itching, and why does it occur?
Itching, also known as pruritus, is a defensive reaction of the body designed to remove parasitic threats and irritating substances from our skin. Our skin, which can cover up to 2 square meters, is the largest organ in our body, serving as the first line of defense exposed to various external factors. Itching is a stimulus that triggers the urge to scratch, often unconsciously. This reaction likely evolved in our ancestors living in open environments to remove parasites and other irritating substances such as thorns or allergens. It turns out that itching can also be contagious, similar to yawning. Since we are social animals, observing others scratching themselves can give us cues for the same behavior.
How does the sensation of itching arise?
Until recently, scientists believed that itching was merely a milder form of pain. However, we now know that itching has its own specialized pathways in our nervous system involving various chemical substances and cells. When something comes into contact with the skin, nerve endings in the epidermis transmit this information to the brain through electrical and chemical signals. Different stimuli activate different nerve pathways, eliciting sensations in the brain. Light touches can be pleasurable, while a blow to the face will likely hurt. However, the exact mechanisms that make itching distinct from other sensations are not yet fully understood.
Why is scratching so pleasurable?
Scratching the skin is technically a form of pain. The term “scratch” literally means “to create a small wound that pierces the skin.” Scratching sends a pain signal to the brain, which suppresses the itch signal, so external stimuli such as hitting or pressing on itchy areas can also provide relief. Remember this when someone tells you not to scratch.
Your brain responds to pain by releasing chemicals in the irritated area, which alleviate the painful sensations. One of these soothing chemicals is serotonin, a neurotransmitter. However, this serotonin also facilitates the re-activation of the itching signal. So, itchy nerves flare up again, and you feel even itchier! Scientists call this continuous itching and scratching cycle the “itch-scratch cycle,” and it can be maddening.
In extreme cases, damage to the sensory nerves for itching can lead to itching without an actual stimulus, a type of itching that scratching cannot relieve. People who have recovered from shingles, a viral infection affecting the nervous system, may experience unexplained, persistent itching after the rash has disappeared. One woman had such an itchy skin after recovering from shingles that she scratched a hole in her head down to her brain (source).
What to do when itching persists. Therapies
Itchy conditions have been documented throughout history, and people have found various ways to alleviate this sensation. The Greeks and Romans used mineral baths and animal fat. Persians used silver. In ancient China, people used menthol, and camphor – a chemical compound extracted from evergreen trees historically used in explosives production – has been soothing itchy skin since the 13th century. Nowadays, we also have anesthetics that numb the skin, anti-inflammatory irritants like capsaicin extracted from chili peppers, and antihistamine drugs and steroid creams. However, due to the diversity of itching causes, there is no universal remedy for everyone. Fortunately, there are many different treatment methods available, so you don’t have to start from scratch. If you experience itching, remember that unlike beauty, itching is not just skin-deep. It is a sensation that reaches from the epidermis to the brain. The origins of this itching you feel now trace back far in the tree of evolution, and we are only scratching the surface of our knowledge about it.
Itching, known as pruritus, is a defensive reaction of the body aimed at removing parasitic threats and irritating substances from our skin. While the precise mechanisms of itching are not yet fully understood, we know that there are specialized pathways in our nervous system responsible for this sensation. Scratching is a way to alleviate itching by triggering painful stimuli that suppress the itch signal. Scientists continue to study these mechanisms to better understand how they work. There are many ways to alleviate itching, both historical and modern, but due to the variety of itching causes, there is no universal cure. Understanding itching is an ongoing research process that allows us to better cope with this unpleasant sensation. It is recommended to consult a doctor or dermatologist in case of severe or chronic itching to receive proper diagnosis and treatment.
Based on material from Dr. Joe Hanson’s channel BeSmart: “Why do we Itch.”
Want to learn more? Check out the sources:
- Niemezjanow G., Szepietowski J. (eds.), Dermatology. Wrocław: Elsevier Urban & Partner, 2019.
- Steinhoff M., Bíró T. (2016). Itch Research and Therapy: Frontiers in Neuroscience. 10. 10.3389/fnins.2016.00146.
- Bhandari S., Caunt C. (2018). Itch-Scratch Cycle: A Neuroimmune Perspective. International Journal of Molecular Sciences, 19(10), 3215.
- Carstens E., Akiyama T. (2010). Itch: Mechanisms and Treatment. CRC Press.
- Neufeld-Cohen A., Tsoory M., Evans A. (2019). Socially induced contagion of itch in mice: A model for empathy? Neuroscience and Biobehavioral Reviews, 105, 104-109.