Breaking Out in Hives: 5 Causes You Wouldn't Expect

If you break out in hives, medically known as urticaria, your skin itches and is covered in red or skin-colored welts. However, it's not always clear what might have triggered them.

Hives typically crop up when you have an allergic reaction to a substance—like pet dander, pollen, or latex—triggering your body to release histamine and other chemicals into your blood. That's what causes the itching, swelling, and other symptoms. Hives can also get worse at night, depending on what a person is exposed to around bedtime, making sleep difficult.

Hives can appear anywhere on the body, including your face, torso, arms, legs, and back, according to the American Academy of Allergy, Asthma & Immunology (AAAAI). They may range from as tiny as a pencil tip to as large as a dinner plate.

The American Academy of Dermatology (AAD) says that hives may last from minutes to hours, typically resolving within 24 hours of their first appearance—though they can last for days or weeks on end. With that in mind, there are two main categories for hives: acute and chronic. Acute hives are those that clear up within six weeks and chronic hives are those lasting more than six weeks, per guidelines published in 2016 in the journal Allergy, Asthma and Immunology Research.

Whether someone falls into the category of acute or chronic hives, there are some concrete causes of those pesky red bumps.

What Are Some Specific Causes of Hives?

Your Diet

If you tend to break out in hives after eating shellfish, peanuts, tree nuts, eggs, milk, and berries, then you may have a food allergy, Debra Jaliman, MD, a New York City-based dermatologist and the author of Skin Rules, told Health.

For some, the culprit is obvious—they'll eat a peanut butter cookie, for example, and immediately break out in a rash. For others, it's not so cut and dry; symptoms can take several hours to develop. Either way, make an appointment with your healthcare provider if you suspect you have a food allergy.

Dr. Jaliman said you'll likely be put on an elimination diet where you reintroduce one potentially triggering food every week. "Let's say you're not eating any of the hives foods, and then you add back shellfish, and you get the hives again. Then you can pretty much figure it out," said Dr. Jaliman. After you determine the culprit, nix it from your diet to prevent mild symptoms from becoming chronic. Dr. Jaliman said you'll likely be prescribed an EpiPen—if you accidentally ingest a trigger food, you could get hives in your throat, which can be dangerous.

The Great Outdoors

Insect bites and exposure to pollen can make you break out in hives, but you probably already knew that. What you may not have realized is that direct sunlight, cold temperatures, or swimming in cold water can also bring on hives, according to the National Organization for Rare Disorders. Hives caused by exposure to heat, cold, or pressure (such as with tight athletic clothing) are a type of physical urticaria, according to the American College of Allergy, Asthma, & Immunology (ACAAI), since the hives have a physical cause.

And this doesn't necessarily mean you're allergic to the elements. "It's really more that your skin is very sensitive," Marilyn Li, MD, a Los Angeles-based allergist and immunologist, told Health.

While avoiding these triggers could prevent hives from returning, Dr. Li said your healthcare provider might be able to provide an antihistamine that could solve weather- or temperature-based problems. That way, you can enjoy a hike on a sunny summer day or hold a cold can of beer on the weekend without worrying about a potential hives outbreak.

An Underlying Illness

Chronic hives can be a telltale sign of a larger problem, according to a study published in 2016 in the journal Therapeutic Advances in Chronic Disease, and extensive blood work may be necessary to pinpoint the underlying issue. Dr. Jaliman said patients with lupus, lymphoma, thyroid disease, and hepatitis might have hives as a symptom of their illness. Since these are typically chronic hives, medications are the most reliable form of relief.

If you've contracted a virus, that could cause hives as well, according to the Asthma and Allergy Foundation of America. Dr. Li said hives caused by viruses typically last six weeks, so if your rash persists for longer, see an allergist to determine another possible cause.

Your Daily Workout

While your morning jog or post-work weightlifting regimen can boost endorphins, your exercise routine could also be causing you to break out in hives. Why? According to Dr. Jaliman, the body produces acetylcholine—a chemical that can inhibit cell breakdown—as a response to exercise. For some people, acetylcholine will disrupt skin cells and either irritate the skin and create a rash the same way histamine does or contribute to the release of histamine, according to a 2021 review article published in Allergology International.

Dr. Li said sweat could also result in a breakout for those prone to hives. The sweat itself doesn't cause hives, but it indicates your body's heat rising. When hives occur due to increased body temperature, it's known as cholinergic urticaria. For some, excess warmth on the skin from a workout or other body-heat-inducing activity is enough to produce hives. "Even taking a hot shower makes them break out," Dr. Li said.

Emotionally Charged Situations

Intense emotional responses can trigger a hives outbreak, according to the ACAAI. For those with chronic hives, or hives that persist for more than six weeks at a time, stress and anger can heat up the body and cause it to release histamine.

"I've seen kids break out in hives from having a temper tantrum," Dr. Li said. "Certainly, stress that's anxiety-related can cause more itching in patients who have hives, and they start to have more hives as a result of itching and scratching the existing ones."

How To Treat Hives—And When To See a Healthcare Provider

In order to get relief from hives, the AAAAI says that the treatments should be geared toward making the hives less itchy and more tolerable, with the ultimate goal of resolving them. Sometimes, treatment can be as easy as avoiding any triggers for the hives. Other treatment options, according to the AAD, may include:

• Anti-itch lotions or creams
• Antihistamines
• Corticosteroids
• Omalizumab (an injectable medication)
• An auto-injector (also known as an EpiPen)
• Light therapy

You may also be able to manage the discomfort that comes with hives by doing things such as avoiding the urge to scratch the affected areas, wearing cotton clothes that are loose-fitting, or taking baths or showers with lukewarm water, the AAD says.

For those with chronic hives from heat-induced or illness-induced activities, Dr. Li suggested visiting a healthcare provider to pinpoint the symptoms and receive an antihistamine prescription. "The solutions are individualized and many times may involve just taking a little more medication," Dr. Li said.

In most cases, hives will go away with time—unless you experience a serious case that may require medication or a shot, according to MedlinePlus. However, if you find that hives are accompanied by symptoms such as mouth or throat swelling, swallowing issues, feelings of faintness, or a racing heart, seek emergency medical attention right away.