Urticaria (hives) is characterized by swollen, red patches on the skin usually as a result of the body’s reaction to certain allergens. It may not be possible to always detect a specific allergen and often a person is allergic to multiple allergens.

A wheal consists of three typical features

  1. Central swelling of variable sizesurrounded by a reflex erythema.
  2. Itching or sometimes burning sensations.
  3. Fleeting nature, with the skin returning to its normal appearance, usually within 1–24 hrs.

Causes

  • Any allergen(food stuff, chemicals, drugs etc) induces release of histamine from the cells lining the blood vessels. In response to this blood plasma leaks out from the small blood vessels into the skin causing the red patches.

Common allergens are

  • Foods: Preservatives and chemical in food. Nuts, chocolate, fish, tomatoes, eggs, milk etc.
  • Medicines: NSAIDS, Aspirin, ACE inhibitors, pain killers etc.
  • Infections & Latex
  • Plants

Symptoms

  • Hives cause itching, burning or stinging sensation and may appear anywhere on the body (skin surface).
  • Angioedema is a severe form of Urticaria and occurs beneath the skin instead of the surface as seen in Urticaria. It results in deep swelling of parts such as the eyes, lips, hands, feet and genitalia. Angioedema affecting the tongue, throat and lungs may be life threatening due to obstruction of the airways. 

Pressure Urticaria

It is a physical Urticaria caused by pressure applied to the skin, and is characterized by the development of swelling, rashes, erythema, stinging sensation and pain.