9th June 2025

Background

Urticaria (hives) is a common cutaneous disorder characterized by well-demarcated raised, erythematous, pruritic welts on the skin. These welts, or “wheals,” vary in size and shape and can appear anywhere on the body. They result from oedema in the dermis as a result of plasma exudate. These wheals can be accompanied by angioedema which, in contrast, are poorly defined areas of swelling of the deeper layers of the dermis, subcutaneous or submucosal tissues of the skin or the mouth. Angioedema is more common around the eyes and lips and is often asymptomatic but can sometimes be painful rather than itchy.

Urticaria can be broadly classified into acute and chronic. Acute urticaria lasts less than six weeks, while chronic urticaria lasts more than six weeks. The exact cause of urticaria is often difficult to determine, but it is thought to be an immune response to a trigger such as an allergen, infection, or physical stimulus. It can occur spontaneously (with no stimulus) or inducible (physical urticaria). The symptoms of physical urticaria are similar to those of other types of urticaria, but they are typically more localized and are triggered by specific physical stimuli. Dermatographism is the most common type of inducible/physical urticaria. Other common types include cholinergic urticaria, a condition that is triggered by an increase in body temperature due to exercise, hot weather, or emotional stress. And primarily driven by the release of acetylcholine which causes small blood vessels in the skin to dilate.

Common drug triggers include aspirin, penicillins, NSAIDs and opiates. These are often termed pseudo-allergens as the urticaria is triggered without a systemic immune response.