Itch
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- For other uses, see Itch (disambiguation)}}}.
Mechanism
The central chemical in itch 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.Itch from cutaneous (skin-related) stimuli, such as movement of small hairs on the body, is transmitted along the same pathway as pain. Itch caused by histamine is transmitted to the brain by a different neural pathway, described in 2001 by Andrew et al. As with pain, histamine-induced itch travels via the spinothalamic tract, but in fibres specific for itch.
Causes
The feeling of itchiness can be caused by movement of hairs or release of a chemical (histamine) from cells under the skin. Itchiness is regarded as protective, as it helps creatures remove parasites that land on them.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)
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; the "itch-scratch itch cycle".A number of plants are known as natural remedies for itch. For mosquito bites, stinging nettles, or poison ivy in the woods the juice of the Jewelweed plant. Others are Dock, traditional for nettle stings. These traditional rememdies often conveniently grows in the areas where the cause (mosquitos, poison ivy, nettles etc) is common.
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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