Hives (Urticaria & Angioedema)

What are hives (urticaria)?

Hives (medically known as urticaria) appear on the skin as wheals which are red, very itchy, smoothly elevated areas of skin often with a blanched center. They appear in varying shapes and sizes, from a few millimeters to several inches in diameter anywhere on the body.

It is estimated that 20% of all people will develop urticaria at some point in their lives. Hives are more common in women than in men. One hallmark of hives is their tendency to change size rapidly and to move around, disappearing in one place and reappearing in other places, often in a matter of hours. Individual hives usually last no longer than 24 hours. An outbreak that looks impressive, even alarming, first thing in the morning can be completely gone by noon, only to be back in full force later in the day. Very few, if any other skin diseases occur and then resolve so rapidly. Therefore, even if you have no evidence of hives to show the doctor when you get to the office for examination, he or she can often establish the diagnosis based upon the history of your symptoms. Because hives fluctuate so much and so fast, it is helpful to bring along a photograph of what the outbreak looked like at its worst.

Swelling deeper in the skin that may accompany hives is called angioedema. This swelling may be seen on the hands and feet, as well as the lips or eyes, that can be as dramatic as it is brief.

What causes hives?

Hives are produced when histamine and other compounds are released from cells called mast cells, which are normally found in the skin. Histamine causes fluid to leak from the local blood vessels, leading to swelling in the skin.

Hives are very common. Although they can be annoying, they usually resolve on their own over a period of weeks and are rarely medically serious. Some hives are caused by allergies to such things as foods, medications, and insect stings, but in the majority of cases, no specific cause for them is ever found. Although patients may find it frustrating not to know what has caused their hives, maneuvers like changing diet, soap, detergent, and makeup are hardly ever helpful in preventing hives and are not necessary for the most part.

Having hives may cause stress, but stress by itself does not cause hives.

In rare cases (some hereditary, others caused by bee stings or drug allergy), urticaria and angioedema are accompanied by a striking decrease in blood pressure (shock) and difficulty breathing. This is called anaphylaxis. Ordinary hives may be widespread and disturbing to look at, but the vast majority of cases of hives do not lead to life-threatening complications.

What does urticaria (hives) look like?