Understanding Pruritus

Localized and Generalized Causes of Itchy Skin

By
Daniel More, MD

Daniel More, MD, is a board-certified allergist and clinical immunologist. He is an assistant clinical professor at the University of California, San Francisco School of Medicine and currently practices at Central Coast Allergy and Asthma in Salinas, California.

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Daniel More, MD
Medically reviewed by
Medically reviewed by Casey Gallagher, MD on October 19, 2020

Casey Gallagher, MD, is board-certified in dermatology. He is a clinical professor at the University of Colorado in Denver, and co-founder and practicing dermatologist at the Boulder Valley Center for Dermatology in Colorado. His research has been published in the New England Journal of Medicine.

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Casey Gallagher, MD
on October 19, 2020
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Pruritus refers to an unpleasant sensation that causes the need to scratch, commonly called itching by most people. Pruritus may be localized to a certain area of the body or can be all over or generalized.

When a rash goes along with the pruritus, it's usually easy to determine the cause and treat it. The most difficult cases of pruritus are those without an associated rash.

Tips for coping with pruritis
Verywell / JR Bee

Biology of Itching

Itching occurs when nerve fibers in the skin send a message to the brain.

Itching and pain are closely related sensations, in that the same nerves transmit both signals to the brain.

In addition to whatever causes an itch in the first place, scratching can often lead to even more itching. This is referred to as the scratch-itch cycle and becomes important in treating the itch no matter the underlying cause.

Pruritus may be caused by a local reaction in the skin (localized pruritus) or a systemic disease that triggers widespread itchiness (generalized pruritus). In some cases, the cause may be psychological or unknown (idiopathic).

Localized Pruritus

When itching occurs on only one part of the body, it is usually caused by a problem in the skin. The specific area of the body that itches may give a clue as to the cause of the itch. Causes of localized pruritus by body part include:

Generalized Pruritus

While generalized itching can be caused by skin conditions, systemic disease is the culprit in up to 50% of cases. Some of the conditions and causes of generalized itching, especially when a rash is not present, include:

  • Allergies, including anaphylaxis and systemic dermatitis
  • Medications, including drug-induced allergies or demyelination (a type of nerve damage)
  • Liver disease, typically in later stages
  • Iron deficiency
  • Neuropathic itch, caused by nerve entrapment or degeneration 
  • Thyroid disease, both hyperthyroidism and hypothyroidism
  • Kidney disease, especially during dialysis
  • Cancer, including leukemias and lymphomas
  • Parasitic infections
  • HIV, especially soon after infection
  • Pregnancy

If you develop generalized itching with or without a rash, your doctor will want to take a careful history and perform a physical exam.

Tests for generalized pruritus may include a complete blood count, kidney function tests, liver function tests, thyroid function test, a stool culture, and an HIV test.

Treatment

The best treatment for pruritus is fixing the underlying cause of itching, whether that's a skin condition or a systemic disease.

Until the underlying problem is corrected, treatment may be needed to control the itch and reduce the itch-scratch cycle. Non-specific treatments for itching include topical steroid creams, oral antihistamines, and good skincare.

Tips for Coping With Pruritus

  • Bathing should be limited to short, cool showers.
  • Only apply soap to the groin, armpits, anal area, under the breasts, and areas of oily skin.
  • Apply a mild moisturizing cream immediately after bathing.
  • Humidify your home to at least 40%, especially during dry, cold months.
  • Avoid contact with wool, fiberglass, detergents, or other topical irritants.
  • Do not scratch.

If you have severe or persistent symptoms of itching, especially generalized pruritus, see your doctor for evaluation and treatment.

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Article Sources
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  1. Twycross R, Greaves MW, Handwerker H, et al. Itch: scratching more than the surface. QJM. 2003;96(1):7-26. doi:10.1093/qjmed/hcg002

  2. Gilchrest BA. Pruritus: pathogenesis, therapy, and significance in systemic disease states. Arch Intern Med. 1982;142(1):101-5. doi:10.1001/archinte.1982.00340140103018

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