Urticaria (hives) is an inflammatory skin disorder in which mediators (mainly histamine) are released from immune cells (mast cells and basophils) in the skin, leading to dilation of blood vessels (redness) and leakage of fluid (swelling). This manifests in the classic itchy, raised, swollen rash of hives. If the swelling occurs deep within the skin tissue where only swelling is obvious, this is known as angioedema. Hives tend to be transitory–individual lesions rarely last more than a day and often change shape and location over the course of minutes to hours.
Approximately fifteen to twenty-five percent of the population will experience hives at some point in their life. Acute urticaria or hives that have been present for fewer than six weeks, might be caused by a variety of triggers including food allergy, drug reactions, viral infections, or insect bites. However, up to fifty percent of cases of urticaria are defined as idiopathic and no cause is ever determined.
Chronic urticaria is much less common. This is a condition in which hives occur for more than six weeks. While many of the same triggers that cause acute urticaria can be implicated in chronic urticaria, a cause is never found in as many as two-thirds of cases. Autoimmunity, in which the immune system makes antibodies against one’s own body, may be an important factor in many of these cases. Autoimmune thyroid disease is particularly common. Chronic urticaria can also be caused by exposure to physical stimuli such as scratching (dermatographism), sweating, pressure, sunlight, heat, water, and cold exposure.
Angioedema can have many of the same triggers as urticaria, including food and medication allergies. ACE inhibitors, which are commonly used to treat blood pressure, are a well-known cause of angioedema. Angioedema reactions can be particularly concerning because they can cause swelling of the airway leading to obstruction and life-threatening breathing difficulties.
Antihistamines are the mainstay of urticaria treatment, blocking the histamine receptors that are responsible for most of the symptoms of hives. Classic first-generation antihistamines such as Benadryl are effective. Still, these are short-acting and cause drowsiness, while the second generation antihistamines including Allegra (fexofenadine), Claritin (loratadine), and Zyrtec (cetirizine) are longer lasting and do not cause drowsiness. Certain medications such as aspirin and NSAID painkillers (ibuprofen and naproxen) should be avoided, as they can make urticaria worse. The biologic treatment, Xolair, represents the newest option for chronic urticaria unresponsive to other treatments. This medication is an antibody that attaches to the allergic antibody, IgE, and prevents IgE from activating mast cells and releasing histamine. A high percentage of patients without response of their urticaria to antihistamines are able to control their symptoms on Xolair.