Why Do I Get Hives in the Sun or Heat?

Does it seem like you’re allergic to the summer? If you experience solar urticaria, your skin develops hives within minutes of being touched by the sun’s ultraviolet rays. Heat urticaria causes the same itchy welts immediately following exposure to heat. While these types of urticaria are often triggered by summer’s hot and sunny weather, hives can be caused by a variety of physical, environmental, and emotional triggers.

Other physical urticarias include hives and skin swelling in response to cold temperatures, vibration (like using a power tool), friction (drying off the skin with a towel), repetitive stretching, and water of any kind at any temperature (called aquagenic urticaria). Stress hives (emotional urticaria) can be triggered by fear, anxiety, and anger.

What causes hives?

Hives are one of the body’s responses to histamine, a chemical released from mast cells and basophils (cells in the blood) in response to a trigger. When histamine is released, histamine receptors respond in various ways, including inflammatory reactions like swollen skin (hives).

How to prevent and treat hives

If you know what typically causes itchy welts to suddenly pop up on your skin, you can make an effort to avoid those triggers to help prevent an outbreak.

If sun and heat give you or your child hives, “I would recommend avoiding the sun,” says Jonette Keri, M.D., Ph.D., a dermatologist at the University of Miami Health System. This can include staying in shaded areas, wearing a hat and UV-protective clothing, and applying sufficient SPF sunscreen to exposed skin before going outside.

“As a first-line treatment, and to prevent the reactions that cause hives, you can use antihistamines (histamine receptor blockers),” she says. “Over-the-counter and prescription topical steroid creams can also help.”

Second-generation antihistamines also are available without a prescription, are effective for up to 24 hours, and do not make most people sleepy. These include Zyrtec (cetirizine), Claritin (loratadine), and Allegra (fexofenadine).

First-generation antihistamines are also available over-the-counter, but last only four to six hours and can cause dizziness and poor coordination. These drugs, including diphenhydramine (Benadryl), are more appropriate if itching keeps you awake at night. Diphenhydramine should not be taken nightly for months at a time.

When to seek medical attention for hives

If the severity or frequency of hives is affecting your quality of life, you may consider a prescription approach with a newer class of medications called biologics.

“For chronic urticaria (chronic hives or those lasting longer than six weeks), we can use an injectable biologic medication, such as omalizumab or dupilumab, which is administered every two or four weeks, depending on the drug,” Dr. Keri says. This type of treatment is also an option for chronic hives triggered by emotional stress.

“Frequent hives are bothersome,” she says. “We are also concerned when patients experience angioedema, which is swelling of the face, tongue, lips, or eyelids. This histamine response can indicate a medical emergency, especially when the larynx is involved, and requires emergency treatment.”

If you live in hot and humid South Florida and would like to see a dermatologist, UHealth providers can diagnose and treat chronic urticaria.

To make an appointment, call 305-243-6704 or request an appointment online.

Written by Dana Kantrowitz. Reviewed by Jonette Keri, M.D., Ph.D.

Tags: Dr. Jonette Keri, histamine, hives, skin care for summer, solar urticaria, summer heat, urticaria