The hives may get bigger, spread, and join together to form larger areas of flat, raised skin.
They can also change shape, disappear, and reappear within minutes or hours. A true hive comes and goes. When you press the center of one, it turns white. This is called blanching.
Your doctor can tell if you have hives by looking at your skin.
If you have a history of an allergy, then the diagnosis is even more obvious.
Occasionally, skin or blood tests are done to confirm that you had an allergic reaction and to test for the substance that caused the allergic response. A skin biopsy can confirm the diagnosis.
Habif TP, ed. Clinical Dermatology. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2009.
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