Urticaria

Definition

A localized or widespread cutaneous hypersensitivity reaction characterized by transient, edematous, pruritic wheals (hives) resulting from mast cell degranulation and histamine release. In medical and veterinary entomology, urticaria is frequently induced by arthropod-derived stimuli: direct envenomation (Hymenoptera stings, caterpillar urticating setae), salivary proteins introduced during hematophagy (mosquitoes, fleas, bed bugs), or contact with defensive secretions and irritating hairs (tussock moth larvae, processionary caterpillars, some tarantula urticating hairs). Lesions typically resolve within hours to days but may persist in chronic forms (>6 weeks) or progress to systemic anaphylaxis in sensitized individuals.

Etymology

From Latin urtica, 'nettle,' referring to the stinging sensation.

Example

Exposure to the urticating setae of the pine processionary moth (Thaumetopoea pityocampa) can cause acute urticaria and ophthalmia in humans and grazing animals; in dogs, contact with caterpillar nests may produce severe lingual necrosis alongside cutaneous wheals.

Synonyms

• hives
• nettle rash

Related Terms

• Urticating hairs
• setae
• hypersensitivity
• anaphylaxis
• envenomation
• dermatitis
• mast cell
• histamine
• Thaumetopoea

Usage Notes

Distinguish urticaria (transient wheals with fluid shift) from papular urticaria (persistent papules, often to arthropod bites) and from contact dermatitis (eczematous, delayed-type hypersensitivity). In entomological contexts, the term often implies IgE-mediated immediate hypersensitivity, though non-immunologic histamine release occurs with some venoms. Chronic urticaria (>6 weeks) warrants investigation for underlying conditions rather than arthropod exposure alone.