Hives, or urticaria, are itchy red bumps that arise when a substance or illness triggers white blood cells in the skin to release histamine. In its attempts to get rid of the offending substance, histamine causes several unpleasant symptoms including swelling, itching, and hives.

While many allergic skin conditions cause itching and redness, hives are uniquely fleeting in nature: A single hive will usually not last longer than 24 hours. New ones may, and often do, appear in the same location or on different parts of the body, but if you were to circle any given hive and check back the next day, it would likely be gone. You can also tell if you have a hive by pressing on it: It will turn white.

That’s different from contact dermatitis, an itchy rash that develops after touching a product to which you’re allergic and lasts for several days, or mosquito bites, which resemble hives but last longer. 

Know your triggers

Several triggers activate the histamine response responsible for acute hives:

Drug allergies. Medication-related hives usually pop up in the first few days of taking a drug. Common culprits include penicillin and other antibiotics (including those containing sulfonamides, also called sulfa drugs), ibuprofen, aspirin and other nonsteroidal anti-inflammatory drugs, anticonvulsants, and chemotherapeutic drugs. New drugs are the most likely culprits. A medication you have been taking for a year or more is an unlikely trigger for a drug allergy.

Food allergies. More than 10 percent of U.S. adults have a food allergy, according to a recent JAMA Network Open study. Shellfish ranks number one. Other common triggers are peanuts, tree nuts, fish, wheat, sesame, soy, egg, and dairy. Many adults with food allergies have had them their entire lives, but about half of food-
allergic adults developed one or more of these allergies as an adult.

Infections. Viral infections such as the common cold, mononucleosis, or even COVID-19 can trigger hives because the immune system kicks in to fight the virus and, in the process, inadvertently activates the histamine-producing mast cells. They can develop at any point in the course of the infection and sometimes even after it has resolved.

Stressors. Intense stress, exposure to extreme cold or heat, and exercise can also trigger hives, especially in people who are already prone to them. They may cluster in areas where there’s physical pressure, like where your pant waistband sits on your hips, under a bra, or where backpack or purse straps hit the shoulder.

Chronic hives

These triggers above are responsible for acute cases of hives, meaning they last a short time. In about 1 percent of the global population, though, hives last six weeks or longer. These are called chronic hives, or chronic spontaneous urticaria (CSU). The diagnosis of CSU is made based on the history and often without any confirmatory testing. Patients are often frustrated, not to mention itchy, uncomfortable, and embarrassed that the hives are so persistent.

Rarely, chronic hives can signal an autoimmune condition such as lupus, rheumatoid arthritis, diabetes, or a thyroid condition. (Other symptoms, such as weight loss or joint pain, will usually also be present if this is the case.) An allergist can diagnose and manage CSU.

Treating acute hives

If hives are accompanied by other allergic reactions, such as throat swelling, difficulty breathing, nausea, vomiting, abdominal pain, or painful, itchy swelling of the eyes, lips, hands, feet or genitals, you should seek urgent medical attention.

If they aren’t accompanied by worrisome symptoms, they can usually be treated at home. Antihistamines are the cornerstone of treatment. While diphenhydramine (Benadryl) is most commonly associated with hives treatment, it’s not the best option. It’s sedating and lasts for only a few hours. Longer-acting, over-the-counter antihistamines like fexofenadine (Allegra) or cetirizine (Zyrtec) are more effective. They block the histamine release responsible for the hives for 12 to 18 hours. Skip the decongestant version of these medications, which are marked with a “D,” (Zyrtec-D), as they can cause rapid heart rate and high blood pressure, especially in older adults.

If you don’t respond to the antihistamine in a day or two, see your primary care doctor, who may prescribe an oral corticosteroid.

Topical steroids aren’t usually effective because an individual hive lasts 24 hours or less, so you’d constantly be playing a game of whack-a-mole trying to get each new one.

Treating chronic hives

For chronic hives that don’t respond to antihistamines and other first-line medications, a monthly injectable medication called omalizumab (Xolair) may be prescribed. Omalizumab limits mast cells’ ability to release histamine. It is generally well-tolerated, and it works so well that the authors of a recent Journal of Allergy and Clinical Immunology study wrote that it has “virtually revolutionized” the treatment of CSU.

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