Itch

From Encyclopedia Jr, free information reference for Kids

For other uses, see Itch (disambiguation).

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. It is a distressing symptom that can cause discomfort. Scratching may cause breaks in the skin that may result in infection. Itching can be related to anything from dry skin to undiagnosed cancer.

[edit] 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, is transmitted along the same pathway as pain. 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.

[edit] 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.

Common causes for itching can be:

• Skin conditions (such as psoriasis, eczema, sunburn and many others). Most are of 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
• Medication:
  • Allergy
  • Photodermatitis – (sun)light reacts with chemicals in the skin, leading to the formation of irritant metabolites
  • Directly (e.g. morphine)

[edit] Treatment

Itching can be treated directly with an antipruritic. Ice can also be helpful. 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".

A number of plants are traditionally seen as natural remedies for itch. For itch caused by mosquito bites, stinging nettles, or poison ivy in the woods, one may use the juice of the Jewelweed plant. Others are Dock, traditional for nettle stings. These traditional remedies often conveniently grow in the areas where the cause (mosquitos, poison ivy, nettles, etc.) is common.

[edit] See also

• Referred itch

[edit] 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.

[edit] External links

• GPnotebook 168165389
• FPnotebook DER266