hives
Meaning of hives: Welts that move: individual patches fade within a day while new ones rise elsewhere, which is what separates them from most other rashes.
Definition of hives
Hives are raised, intensely itchy welts that appear suddenly on the skin, often in crops that shift position over hours. On lighter skin they usually look pink or red; on darker skin they may match the surrounding skin tone or look slightly darker, so the raised, swollen feel is more reliable than color. Any single welt normally fades within a day.
What is happening in the skin?
Mast cells sit throughout the skin loaded with chemical messengers, of which histamine is the best known. When they release their contents, small blood vessels in the upper skin widen and leak fluid into the surrounding tissue. The trapped fluid lifts the surface into a welt and irritates the nerve endings that carry itch. The leak is temporary, the fluid drains away, and that welt disappears while another forms nearby. Where the same process happens in the deeper layers, it produces angioedema, a puffy swelling of the lips, eyelids, hands or feet that feels tight or painful rather than itchy and can accompany hives.
What sets them off?
An allergic response to a food, a medicine or an insect sting is the familiar trigger, and in that case the immune system has recognized the substance and instructed the mast cells to fire. Mast cells can also release histamine without any immune recognition at all, prompted directly by certain drugs or by physical pressure, which is why not every episode of hives is an allergy. Infections are a frequent cause, particularly in children. Physical triggers include heat, cold, sunlight, exercise, sweating, vibration and firm stroking of the skin. Many episodes have no identifiable cause despite investigation.
How does the acute form differ from the chronic one?
| Acute | Chronic | |
|---|---|---|
| Duration | Under about six weeks | Recurring most days beyond about six weeks |
| Usual cause | Often traced to a food, drug or infection | Frequently no external trigger is found |
| Investigation | Guided by the history | Directed at other conditions rather than at allergy testing |
The chronic form is often driven by the immune system acting against the person's own mast cells, which is why hunting for an allergy in these cases usually finds nothing. Hives accompanied by swelling of the tongue or throat, difficulty breathing or faintness point toward a severe whole-body reaction rather than a skin problem alone.
Also known as
Used in a sentence
The patient developed hives across the trunk shortly after starting the new medication.
Good to know
Acute hives lasting under about six weeks are often traced to a specific trigger, while chronic hives persisting beyond that period frequently have no external cause identified, and redness is an unreliable sign on darker skin where welts may match the surrounding tone.