Understanding Pruritus

Localized and Generalized Causes of Itchy Skin

Hand feeling rash on arm
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Pruritus refers to an unpleasant sensation that causes the need to scratch, commonly called itching by most people. Itching may be localized to a certain area of the body or can be all over or generalized. When there is a rash that goes along with the pruritus, the cause is often easily determined and treated. However, the most difficult cases of pruritus are those without an associated rash.

Biology of Itching

Itching occurs when nerve fibers in the skin send a message to the brain via nerves. Itching and pain are closely related sensations, in that the same nerves transmit both signals to the brain.

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).

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.

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 around 50 percent 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)
  • Liver disease (typically later-stage disease)
  • 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 (commonly experienced soon after infection)
  • Pregnancy

If you develop generalized itching with or with 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 of pruritus is to fix the underlying cause of the itching, whether that is 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 skin care.

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 least 40 percent, 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 appropriate evaluation and treatment.

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