Hives, medically known as urticaria, are itchy, raised welts on the skin. These welts vary in size, from small bumps to larger patches, and may be red or skin-colored. Hives arise from various internal and external factors, including allergic reactions and infections. Environmental elements, such as heat, are often considered potential triggers or aggravators.
Heat’s Influence on Hives
Heat can worsen or trigger hives through several mechanisms. When the body is exposed to warmth, blood vessels in the skin dilate (vasodilation). This increased blood flow can heighten the inflammatory response, making existing hives more pronounced or encouraging new ones to form.
The body’s response to heat also involves sweating, which can contribute to hive flare-ups. A rise in body temperature can prompt histamine release. This causes swelling, redness, and itching, hallmarks of hives. While heat may not be the direct cause of all hives, it can certainly act as a significant exacerbating factor.
Specific Hives Triggered by Heat
Beyond aggravating hives, heat can directly trigger specific types of urticaria. Cholinergic urticaria (CU) is a common “heat hives” form occurring when the body’s core temperature rises. This can be due to exercise, hot baths, emotional stress, or consuming spicy foods. Symptoms of CU involve small, itchy, prickly or burning bumps, often surrounded by redness, appearing within minutes of a temperature increase and usually fading within an hour. This reaction is thought to involve an immune overreaction to acetylcholine, a chemical messenger released by the nervous system in response to sweating.
Another type is heat urticaria, also known as contact heat urticaria. This condition is distinct from cholinergic urticaria, triggered by direct skin contact with a warm stimulus, not a rise in core body temperature or sweating. Examples include touching a hot object, holding a warm drink, or exposure to hot air. The hives appear rapidly in the area of contact and resolve within one to two hours. Unlike cholinergic urticaria, heat urticaria does not involve sweat gland activation.
Managing Hives in Warm Conditions
Managing hives when heat is a factor involves strategies to keep the body cool and minimize triggers. Cool showers or baths can help lower skin temperature and provide itching relief. Using air conditioning and seeking shade are also effective ways to avoid overheating.
Wearing loose-fitting, breathable clothing, such as cotton, helps prevent heat and sweat accumulation on the skin, reducing irritation. Staying well-hydrated by drinking plenty of fluids is important, especially in warm environments. Over-the-counter antihistamines alleviate itching and reduce swelling by blocking histamine’s effects. These medications are available in non-drowsy formulations. Applying a cool compress to affected areas can offer temporary relief.