Hives

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Eczema · Atopic Dermatitis
Hives and eczema both itch and are often confused, but they work differently. In hives, mast cells release histamine and small vessels leak plasma into a wheal, and each wheal usually fades within 30 minutes to 24 hours; eczema starts with a skin barrier that cannot hold water and an immune tilt toward type-2 inflammation, and its rash persists and flares again and again.

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What hives are

THE SHORT ANSWER

A wheal forms when skin mast cells release histamine and small vessels leak plasma; each one usually fades within 30 minutes to 24 hours while new ones appear elsewhere.

WHAT IT MEANS FOR YOU

Hives with swelling of the lips, tongue or throat, a tight throat, trouble breathing or feeling faint: call emergency services now.

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READ THE ORIGINAL

Hives, or urticaria, happen when mast cells in the skin suddenly release histamine and other substances: a small patch of blood vessels widens and leaks plasma, and the skin rises into a sharply edged, itchy bump called a wheal, often ringed with redness. Hives come fast and go fast. A single wheal usually fades within 30 minutes to 24 hours and the skin returns to normal, but new ones can appear elsewhere, so the rash seems to move around.

Hives are common: an international guideline estimates that about 20% of people have acute hives at some point in life. Hives that last 6 weeks or less are called acute; they often follow a cold, a food or a medicine, though in about half of cases no cause is found. Hives that last more than 6 weeks are called chronic. The kind that appears on its own usually has no outside cause, and in more than half of these people it is tied to the immune system attacking the body itself.

One situation cannot wait a minute: if hives come with swelling of the lips, tongue or throat, a tight throat, trouble breathing, or feeling faint, this may be anaphylaxis, a severe allergic reaction. Call emergency services now; what to do is in When to get emergency or medical help.

Educational content, not medical advice — consult a clinician.

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