Table of Contents
Definition of Pruritus
Pruritus is a symptom of innumerable health conditions and may be localized (confined to a specific area or to lesions) or generalized (widespread, involving much of the skin’s surface).
The skin may appear reddened (erythema), swollen (edema) or otherwise irritated, or may show no reason for the itching.
Reasons for Itchy Skin
The physiologic mechanism of itching is similar to, though distinctive from, that of pain. The nerve cells, called nociceptors, that send itch signals to the brain are scattered throughout the epidermis and upper layer of the dermis.
Irritants that contact the epidermal and dermal layers of skin can arouse the nociceptors, coming from the external surface of the skin (such as from lesions that form on the skin) or from within (such as the accumulation of bilirubin, which accounts for the itching that accompanies jaundice). Histamine, which the immune system releases during a hypersensitivity reaction (allergy or asthma), is among the internal stimuli that activate these nociceptors.
Pruritus and Scratching
The response of scratching is a reflex that the autonomic nervous system generates in response to itch signals. Researchers theorize that scratching activates a mild pain response that overrides the itch response. Pain and itch appear to use many of the same nociceptors, and pain seems to be the more dominant stimulus. However, many factors contribute to the experience of itching as well as to its relief.
Scratching is also a conscious action, and can itself be an irritant that causes itching. Dermatologic conditions in which the itch/scratch relationship becomes circular include lichen simplex chronicus and prurigo.
Health Conditions Associated with Pruritus
Indication of Systemic Health Conditions
Pruritus is often an early indication of systemic health conditions such as jaundice or kidney dysfunction, and is a hallmark symptom of dermatologic conditions such as psoriasis and dermatitis. The diagnostic path depends on the complex of symptoms.
Treatment may include topical or systemic antihistamine medications or corticosteroid medications and other therapies to resolve the underlying condition. It is important to resist the urge to scratch, as scratching further irritates the skin and may open the pathway for infection.
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