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What is an itch and why do we get itchy?

Do you often wonder why you get itchy? Learn about the science behind itching and what causes it.

What is an itch and why do we get itchy?

Itching is a sensation caused by specialized nerve endings in the skin. It can be triggered by a wide range of factors, including allergens, parasites, dry skin, diseases, psychiatric issues, and nerve damage. Here's what you need to know about itching and why we get itchy.

The science behind itching

An itch is a sensation caused by a stimulation of specific nerve endings called pruriceptors that are only there to produce an itchy feeling in the skin. Itchiness is a signal your brain sends to let you know that something that is irritating the skin.

When the skin is exposed to an allergen or a toxic chemical, it triggers the release of histamines. These histamines boost blood flow to the affected area, resulting in inflammation and the release of chemicals from your immune system. The inflammation then stimulates the pruriceptors.

Common causes of itching

Itchiness is an evolutionary advantage to help us protect our skin against toxins and critters, but there are other reasons we get itchy.

Generally there are five main causes of itchiness:

  1. Contact with an allergen or parasite: Your body is on alert at all times for intruders and toxins from the outside world. So when your body senses an allergen (like mosquito bite) or some other toxic chemical (like poison ivy), it triggers the release of histamines. Histamines boost blood flow to the affected area which creates inflammation and delivers chemicals from your immune system. The inflammation stimulates the pruriceptors, resulting in an itchy feeling.

  2. Dry skin: When skin gets dry, it becomes more rigid and this increased friction results in microfractures. To heal the fractures, your body increases blood flow which results in inflammation. This inflammation again stimulates the pruriceptors, resulting in an itchy feeling.

  3. Certain diseases: Diseases like liver disease, kidney disease, anemia, diabetes, thyroid problems and certain cancers have been known to cause itchiness. The reasons vary but are primarily due to either a build up of toxins in the skin or a chemical imbalance that causes dry skin.

  4. Psychiatric issues: More frequent itchiness is associated with people who have heightened stress, anxiety, obsessive-compulsive disorder, and other mood disorders. The "psychogenic itch" is not well understood at this time, but it's thought to be related to increased stress levels making it difficult for the brain discriminate between itch-worthy and non-itch-worthy stimuli, along with the potential for a feedback loop of pleasure that results from scratching an itch.

  5. Nerve damage: Nerve damage can cause itching for a number of reasons. It can affect the way that the brain processes sensations from the skin, leading to sensations of itching even when there is no stimulus present. In other cases, nerve damage can cause changes in the way that the skin responds to irritants, leading to itching as a result. Additionally, nerve damage can also lead to decreased blood flow in the affected area, which can cause itching due to dry skin.

Why does scratching feel good?

When you go to scratch that itch, you're rubbing not only pruriceptors but also other pain and touch nerve endings. This sends mixed signals to your brain which results in temporary relief. But as soon as you stop scratching, the itch will return. It's tempting to scratch for the momentary respite from the itch, but it's best to keep your hands off as scratching may cause the skin to become even more irritated.

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Sources

Andrews, M. A. W. (2007, March 26). Why and how do body parts itch? Why does it feel good to scratch an itch? Scientific American. Retrieved February 8, 2023, from https://www.scientificamerican.com/article/experts-why-we-itch-and-scratch/

Fowler, P. (2022, August 14). What Are Histamines? WebMD. Retrieved February 8, 2023, from https://www.webmd.com/allergies/what-are-histamines

Johns Hopkins University. (2021, August 8). How Wounds Heal. Johns Hopkins Medicine. Retrieved February 8, 2023, from https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/how-wounds-heal

Mayo Foundation for Medical Education and Research. (2023, January 14). Itchy skin (pruritus). Mayo Clinic. Retrieved February 8, 2023, from https://www.mayoclinic.org/diseases-conditions/itchy-skin/symptoms-causes/syc-20355006

Misery, L., Dutray, S., Chastaing, M., Schollhammer, M., Consoli, S. G., & Consoli, S. M. (2018, March 1). Psychogenic itch. Nature News. Retrieved February 8, 2023, from https://www.nature.com/articles/s41398-018-0097-7