Cholinergic Urticaria: The Hives from Heat or Sweat

Cholinergic urticaria refers to small, red, itchy hives that appear when your body temperature rises and you begin to sweat. This reaction often occurs during exercise, hot showers, emotional stress, or even after eating spicy foods. It’s an immune response triggered by heat, also known as heat hives or heat bumps.

The word “cholinergic” refers to acetylcholine—a chemical messenger released by the parasympathetic nervous system. Meanwhile, “urticaria” is the medical term for hives or skin welts. Cholinergic urticaria commonly affects people between the ages of 10 and 30.

Who Gets Cholinergic Urticaria?

Hives affect about 1 in 5 people at some point in their lives. Cholinergic urticaria makes up around one-third of all physical hives caused by triggers like heat, pressure, or cold. Moreover, about 0.7% of people with chronic hives experience symptoms of cholinergic urticaria. Although common, it can still affect daily life and requires proper management for comfort and relief.

What Causes Heat Urticaria?

Heat urticaria is triggered when your skin comes into direct contact with heat. This causes your body to release certain chemicals, like histamine, that lead to redness, swelling, and itching in the affected area.

Common Triggers Include

• Submerging a limb in warm water
• Standing close to a gas stove while cooking
• Using a hairdryer or sitting under hot sun
• Resting against a hot water bottle or heater
• Eating or drinking very hot food or beverages

How Does It Happen?

When heat touches your skin, mast cells (a type of immune cell) become active. These cells release histamine and other substances that cause:

• Blood vessels in your skin to widen
• Swelling
• Redness
• Itchy, raised welts (known as wheals)

Heat Urticaria vs. Cholinergic Urticaria

• Heat urticaria is triggered by direct heat exposure on the skin.
• Cholinergic urticaria is triggered by sweating due to activities like exercise or hot showers.
• Heat urticaria doesn’t involve the body’s core temperature or sweat glands—unlike cholinergic urticaria.

Cholinergic Urticaria Symptoms

Cholinergic urticaria (CU) causes itchy, tingly, and warm hives. These hives are small—about 1–3 millimetres—and appear with red flares or circular wheals around them.
They can show up anywhere, but they mostly affect the chest, face, upper back, and arms. In many cases, the bumps cluster together, making the skin look flushed, blotchy, or swollen. These hives usually appear within six minutes of a trigger, like heat or exercise. They typically fade away within 30 minutes to two hours.

Additional Symptoms

Besides hives, some people may also experience:

• Wheezing
• Diarrhea
• Excess saliva
• Rapid heartbeat
• Headache
• Low blood pressure
• Light-headedness
• Stomach cramps
• Shortness of breath

Although not common, these symptoms can occur, especially if the reaction is more intense.

How to Diagnose Cholinergic Urticaria?

If your symptoms are not severe but disrupt your daily life, consult your doctor. In many cases, a simple discussion and physical evaluation are enough to diagnose cholinergic urticaria (heat hives). However, your doctor may recommend a few tests to confirm the condition and rule out other issues.

Common Diagnostic Tests

1. Passive Warming Test

Your body temperature is raised using warm water or by staying in a heated room.
The doctor watches for hives or other symptoms during the process.

2. Methacholine Skin Challenge

A small amount of methacholine (a medication) is injected into your skin. The doctor checks for a reaction. However, not everyone with CU reacts to this test, so it may be used alongside other tests.

3. Exercise Challenge Test

You perform physical activity under supervision while your doctor observes for symptoms. In some cases, additional instruments are used to monitor your response.

Cholinergic Urticaria Treatment and Prevention

Cholinergic urticaria often gets better with age, and in some cases, it may go away on its own after a few years. Until then, your doctor may suggest treatments to control your symptoms and prevent flare-ups.

Common Treatment Options

• Antihistamines – Help reduce itching and swelling
• Asthma medications – May be helpful in some cases
• Blood pressure medications – Certain types can ease symptoms
• Anticholinergics – Reduce sweating, which can lower the risk of hives

Prevention

You can’t stop your body from sweating—it’s necessary for temperature control and overall health. However, you can lower the chances of triggering heat hives by making a few lifestyle changes.

Helpful Prevention Tips

• Avoid spicy foods that increase body heat
• Exercise when it’s cooler—early morning or evening
• Manage stress and anxiety with calming activities
• Do not take hot showers or baths
• Wear lightweight, breathable clothes that wick away sweat

Other Types of Urticaria

Acute Urticaria

Acute urticaria is a short-term type of hives that lasts less than six weeks. It’s usually triggered by allergic reactions to food, medications, insect bites, infections, or stress. The symptoms include sudden, itchy welts or swelling on the skin, which often resolve quickly once the trigger is removed.

Chronic Urticaria

Chronic urticaria lasts longer than six weeks and may persist for months or even years. In many cases, the cause remains unknown (idiopathic), though it may sometimes be linked to autoimmune conditions. Symptoms include hives that repeatedly appear and disappear, often accompanied by deeper swelling known as angioedema. To improve treatment outcomes, clinical trials are currently underway to explore potential solutions for chronic urticaria.

Urticaria Multiforme

Urticaria multiforme is a type of short-term (acute) allergic skin reaction. It happens when your body releases a chemical called histamine, which can be triggered with or without an allergy (IgE-dependent or independent). The hives are usually ring-shaped or have overlapping circles. They often look red or purplish and turn white when you press on them.

Aquagenic Urticaria

Aquagenic urticaria is a very rare condition where contact with water—regardless of temperature—causes small, itchy hives to appear. Even brief exposure, such as bathing or sweating, can trigger a reaction. The exact cause isn’t well understood, and managing it often involves antihistamines and minimizing skin contact with water when possible.

Urticaria Pigmentosa

Urticaria pigmentosa is a form of cutaneous mastocytosis most commonly seen in children. It involves an abnormal buildup of mast cells in the skin, leading to brownish lesions that can become raised, red, and itchy when scratched or rubbed. These spots can persist for years but may fade over time, especially in paediatric cases.

Papular Urticaria

Papular urticaria is a skin reaction to insect bites, more common in youngsters and often seen in summer or fall. It causes small, raised, itchy bumps that are pink, red, or brown. These bumps usually appear in clusters and can cause significant discomfort.

Conclusion

In conclusion, cholinergic urticaria, though common, can significantly impact daily life, but with proper diagnosis and treatment, symptoms can be managed effectively. Cholinergic urticaria may improve over time. Lifestyle changes and treatments such as antihistamines or anticholinergics can help manage flare-ups. Furthermore, ongoing research is focused on discovering more effective treatment options for better symptom control.