Urticaria and angioedema

Dr Michael Radcliffe explains the difference between urticaria and angiodema:

I work in a busy NHS allergy clinic in central London and in a full day of seeing patients in the out-patient clinic, I will typically see 10 new referrals. The commonest reason for being referred is a condition called urticaria. Amongst 10 new referrals I will expect to make this diagnosis 3 or 4 times.

But what is it and what causes it?  Some peoples call it hives, or welts or stinging nettle rash.  The last name is closest to the truth.  The Latin word for the stinging nettle is Urtica and so Urticaria is Latin for the itchy rash that occurs when someone brushes against stinging nettle leaves, the hairs of which are rich in plant histamine, whereas urticaria occurs when human histamine is released without good reason from immune system cells called mast cells in the skin and mucous membranes.

Urticaria causes transient, itchy skin blotches that are called wheals.  Urticarial wheals may appear singly, or a rash may form when wheals are constantly coming and going.  By comparison, angioedema causes non-itchy, pale or pink swellings that are more deep-seated and arise around the eyes, lips, face or anywhere on the body.  Urticaria and angioedema are common conditions, affecting 1 in 5 people at some time in their lives. Urticaria may occur alone (50% of cases), with angioedema (40% of cases), or angioedema may occur alone (10% of cases).  There is a common misunderstanding that the most likely cause of these conditions is a hidden allergy.   Surprisingly this is very rarely found to be true.  Whilst an allergic reaction to a food (e.g. nuts), a sting venom (e.g. a wasp sting) or a drug (e.g. penicillin) can lead to urticaria, it typically arises in combination with other allergic symptoms or, in extreme cases, as one part of the life-threatening condition known as anaphylaxis.  Moreover, in cases where urticaria occurs due to food, insect sting venom or a drug or medicine, the relationship is usually obvious and not in doubt.

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Next review: 20 February 2021