[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Skin](https://durgical.com/en/general-pathology/areas/skin/) › Urticaria and angioedema

# Urticaria and angioedema

- Lesion

Hives are itchy wheals that come and go within hours. Mast cells release histamine, which makes small vessels leak.

Updated Nov 12, 2026

## Key points

- IgE-dependent: allergens (foods, drugs, insect venom) cross-link IgE on mast cells: type I hypersensitivity.
- IgE-independent: direct mast cell degranulation (opioids, radiocontrast), NSAIDs (arachidonic acid shift), physical triggers (cold, pressure, heat).
- Chronic spontaneous urticaria: often autoantibodies against IgE or the high-affinity IgE receptor.
- Biopsy is subtle: dermal oedema, dilated lymphatics, sparse perivascular mononuclear cells and eosinophils; epidermis normal.
- Bradykinin angioedema (hereditary C1 inhibitor deficiency, ACE inhibitors) has no wheals or itch and does not respond to antihistamines.
- Urticarial vasculitis: wheals lasting more than a day with bruising; leukocytoclastic vasculitis on biopsy.

## What it is

Urticaria is a localised, transient dermal oedema caused by mast cell degranulation. Individual wheals usually fade within a day, and the episode is acute if it lasts under six weeks and chronic if longer. Angioedema is the same process deeper in the dermis and subcutis; when it occurs without wheals, bradykinin-mediated causes such as C1 inhibitor deficiency or ACE inhibitors must be considered.

## Step by step

- A trigger activates mast cells (IgE cross-linking or a direct stimulus).
- Granules release histamine, and the cell makes prostaglandin D2 and leukotrienes.
- Histamine on H1 receptors makes venules leak and nerves itch.
- Plasma leaks into the superficial dermis (wheal) and the reflex axon dilates nearby vessels (flare).
- Fluid is reabsorbed within hours, so the wheal disappears without a mark.

## Clinical notes

- Wheals lasting more than a day, burning rather than itch, or residual bruising suggest urticarial vasculitis.
- Angioedema of the larynx can obstruct the airway.

## Memory aid

A hive is a water balloon filled by histamine that drains by tomorrow; if it lingers and bruises, look at the vessel walls.

## Test yourself

Think of the answer, then tap the question to see it.

## What is seen on biopsy of ordinary urticaria?

Superficial dermal oedema, dilated lymphatics and sparse perivascular lymphocytes and eosinophils; the epidermis is normal.

## Why does hereditary angioedema not respond to antihistamines?

It is mediated by bradykinin, from uncontrolled kallikrein activity due to C1 inhibitor deficiency, not by histamine.

## What are two IgE-independent triggers of urticaria?

Opioids or radiocontrast (direct mast cell activation) and NSAIDs; also physical triggers such as cold or pressure.

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## Elsewhere in DurgiPedia

- [Type I hypersensitivity (immediate, IgE)](https://durgical.com/en/immunology/type-i-hypersensitivity/)
- [Mast cell and basophil](https://durgical.com/en/immunology/mast-cell-and-basophil/)
- [Histamine, serotonin, bradykinin and the plasma protein cascades](https://durgical.com/en/general-pathology/histamine-serotonin-bradykinin-and-the-plasma-protein-cascades/)

## Connections

## Related 3

- [Eczematous dermatitis](https://durgical.com/en/general-pathology/eczematous-dermatitis/)
- [Mycosis fungoides, Sézary syndrome and mastocytosis](https://durgical.com/en/general-pathology/mycosis-fungoides-sezary-syndrome-and-mastocytosis/)
- [Histamine, serotonin, bradykinin and the plasma protein cascades](https://durgical.com/en/general-pathology/histamine-serotonin-bradykinin-and-the-plasma-protein-cascades/)

## Related conditions 2

- [Urticaria and angioedema](https://durgical.com/en/conditions/urticaria-and-angioedema/)
- [Mastocytosis (cutaneous and systemic)](https://durgical.com/en/conditions/mastocytosis/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Hives](https://medlineplus.gov/hives.html) (MedlinePlus, US National Library of Medicine, 2025).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/urticaria-and-angioedema/