Urticaria

Urticaria (Hives): Mechanism of Onset

Urticaria is a common skin condition characterized by the sudden appearance of itchy, pale‑pink wheals (hives) surrounded by a zone of redness. These lesions resemble "stings" from nettles, which is the origin of the name. The key feature of urticaria is its ephemerality: an individual wheal usually lasts no more than 24 hours, disappears without a trace in one spot and may appear elsewhere. It is not a standalone disease, but a type of skin allergic reaction to various triggers.

What happens in the skin?

The basis of urticaria is degranulation of mast cells — specialized immune cells located in the skin. In response to a certain stimulus they instantly release large amounts of histamine and other inflammatory mediators into surrounding tissues. Histamine produces three main effects:

1. It dilates small blood vessels (arterioles), leading to redness (erythema).
2. It increases vascular permeability, allowing plasma to leak into tissues and form swelling — the wheal itself.
3. It irritates nerve endings, causing intense itching.

Causes and triggers of urticaria

Depending on duration, urticaria can be acute (up to 6 weeks) or chronic (over 6 weeks).

• Acute urticaria: Most often has a clear cause.
  • Infections: Viral infections are the most common cause in children.
  • Food allergy and drug allergy.
  • Insect stings.
• Chronic urticaria: In 80‑90 % of cases the cause cannot be identified (chronic spontaneous urticaria). It is considered to have an autoimmune nature. Sometimes physical factors such as pressure, cold, heat, or sunlight can act as triggers.

Read more about this condition in children in the article "Urticaria in Children".