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Hives (urticaria) can erupt unexpectedly and can disappear just as suddenly. It can be difficult to recognize hives because they vary greatly in their appearance. They may be:

• Alone or in batches
• Arranged randomly or in a vertical row
• Burning, stinging or itchy
• Circular or irregularly shaped
• Red, pink or white
• Slightly raised or flat and smooth
• Varying sizes (as small as a pencil eraser or as large as a basketball)

Unlike other skin rashes, hives are not flaky. An individual hive (called a wheal) also differs from a blister, which has a loose membrane over liquid. Wheals usually remain less than a half-inch (1 centimeter) across. Those that are larger (up to 4 inches across, or 10 centimeters) may look like rings of redness with a pale center. Wheals cannot break apart and liquid does not ooze out. They generally cluster and rise in one area and then wane only to reappear in a batch somewhere else on the body. Wheals can change shape and disappear or reappear within minutes or hours. Typically, a wheal lasts only a few hours before fading away. They do not leave a mark on the skin after they subside.

The most frequent complaint is the annoying itch that accompanies wheals, but they can also cause a burning or stinging sensation. The eruptions may be so intense that they lead to extreme irritability and sleeplessness. Although the itch associated with hives can be severe, the skin is not usually broken or scabbed.  

Most hives are white or red welts that are surrounded by a red patch (called a flare) on the skin’s surface, quite often where clothes touch the skin. Deep swelling beneath the skin that appears on the face (particularly the lips and eyelids), tongue, extremities or genitals is a related condition called angioedema. Less often it occurs around the hands, feet and throat. Angioedema, though related to hives, has a different appearance:

• Eyes may appear swollen closed
• Skin surface may appear normal (no hives or rash)
• Swellings may appear the same on both sides of the body
• Swellings usually do not itch, but may cause pain or a burning sensation

Hives are rarely life-threatening, and acute cases usually disappear on their own. However, more severe reactions may accompany hives or angioedema. Potentially life-threatening reactions are called anaphylaxis and require immediate medical care. Signs and symptoms of anaphylaxis include:

• Difficulty breathing and swallowing
• Dizziness or faintness
• Loss of consciousness
• Rapid or abnormal heartbeat
• Swelling of the face, tongue or throat