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An 'itch' (Latin: 'pruritus') is a sensation felt on an area of skin that causes a person or animal to desire to scratch that area. Itching can be related to anything from dry skin to cancer.

Contents

Mechanism

Causes

Treatment

See also

References

External links

Mechanism

The central chemical involved in itching is histamine, a molecule released by mast cells in the skin. Histamine is the chemical that causes the itch and reddening when bitten by insects. It binds to local nerve endings on specific receptors.
An itch from cutaneous (skin-related) stimuli, such as movement of small hairs on the body, was thought to be transmitted along the same pathway as pain, although recent research has found that itching has its own neural pathways. An itch caused by histamine is transmitted to the brain by a different neural pathway, described in 2001 by Andrew ''et al''. As with pain, a histamine-induced itch travels via the spinothalamic tract, but in fibres specific for itch.

Causes

The feeling of itchiness can be caused by a movement of hairs or the release of a chemical (histamine) from cells under the skin. Itchiness is regarded as protective, as it helps creatures remove parasites that land on their skin.
Itching can be caused by:

★ Xerosis. This is the most common cause, frequently seen in winters. Associated with older age, frequent bathing in hot showers or baths, and high temperature and low humidity environments.

★ Skin conditions (such as psoriasis, eczema, sunburn, athlete's foot and many others). Most are of an inflammatory nature.

★ Insect bites, such as those from mosquitos or chiggers.

★ Allergic reactions to contact with specific chemicals, such as Urushiol from Poison Ivy or Poison Oak.

★ Hodgkin's disease

★ Jaundice (bilirubin is a skin irritant at high concentrations)

★ Polycythemia, which can cause generalized itching due to increased histamine

★ Scabies or infection with lice or worms

★ Thyroid illness

★ Diabetes Mellitus

★ Dandruff

★ Iron deficiency anemia

★ Parasitic infections

★ Psychiatric

★ Medication:

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★ Allergy

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★ Photodermatitis – (sun)light reacts with chemicals in the skin, leading to the formation of irritant metabolites

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★ Directly (e.g. morphine)

★ Cholestasis

★ Related to pregnancy:

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★ Pruritic Urticarial Papules and Plaques of Pregnancy (PUPPP)

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★ Gestational pemphigoid

Treatment

Main articles: Antipruritic

A variety of over-the-counter and prescription anti-itch drugs are available. Some plant products have been found to be effective anti-pruritics, others not. Non-chemical remedies include cooling, warming, soft stimulation.
Sometimes scratching relieves isolated itches, hence the existence of devices such as the back scratcher. Often, however, scratching can intensify itching and even cause further damage to the skin, dubbed the "itch-scratch-itch cycle".
The mainstay of therapy for dry skin is maintaining adequate skin moisture and topical emollients.

See also

★ Referred itch

★ Personal grooming

★ Anti-itch drug

References

★ Andrew D, Craig AD (2001). Spinothalamic lamina I neurons selectively sensitive to histamine: a central neural pathway for itch. ''Nature Neuroscience'' Jan;4(1):9-10.

★ National Cancer Institute (2003) "Pruritus" Retrieved Aug. 22, 2005.

External links

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