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Cholinergic Urticaria: A Lesser-Known Sweat Allergy

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By Editorial Team

3 min read

Reviewed by: HU Medical Review Board | Last reviewed: May 2023

Cholinergic urticaria (CholU) is a relatively common allergic reaction, but many people do not know about it. CholU is when your skin reacts to sweating or an increased body temperature. There are other types of CholU that involve decreased or no sweat.1

People with cholinergic urticaria get a rash whenever they sweat or feel warm. This could be caused by:1

  • Exercise
  • Hot showers
  • Warm weather
  • Strong emotions

The symptoms of CholU usually go away within an hour. But people living with the condition report that it significantly affects their quality of life.1

What are the symptoms of CholU?

The rash caused by CholU looks like small, very itchy, raised red dots. This rash appears on the skin when the body’s core temperature increases, causing sweating. Many people living with CholU report stinging pain or itching at the site of the rash. The most common place the rash is seen is on the trunk. But it can happen anywhere on the body except:1

  • Palms of hands
  • Soles of your feet
  • Underarms

CholU can also cause severe symptoms. These include angioedema (swelling of the face and throat), difficulty breathing, and anaphylaxis (severe, life-threatening allergic reaction.) CholU affects women and men equally. But women are more likely to have severe reactions like anaphylaxis.1

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What causes cholinergic urticaria?

CholU affects up to 20 percent of young adults in their 20s and 30s. In the general population, CholU affects 4 to 11 percent of people.1

Experts are not completely sure what causes the rash. But they do know that CholU, like most allergies, is an immune system response. When immune cells called mast cells are activated, they release a substance called histamine. Histamine is responsible for symptoms like angioedema and anaphylaxis.1,2

What are the subtypes of CholU?

Experts have found that CholU can be divided into 4 different categories. Each category or subtype looks a bit different and has a slightly different cause. Understanding the subtypes can help doctors find the best treatment for you.3

Conventional sweat allergy-type CholU

This type of CholU is caused by an allergy to sweat. This is a traditional allergy like someone would have to pollen or certain foods. When sweat touches the skin, immune cells release histamine. This causes the CholU symptoms.3

Follicular-type CholU with positive autologous serum skin test

People living with this subtype develop the rash without a traditional sweat allergy. With this subtype, the rash appears specifically around hair follicles.3

CholU with palpebral angioedema

This subtype is similar to the first because it is also a traditional sweat allergy. But a person with this subtype experiences swelling around the eyes and eyelids (called “palpebral angioedema”). People with this subtype are much more likely to be female and to experience anaphylaxis.3

CholU with acquired anhidrosis and/or hypohidrosis

People with this subtype sweat less than the average person (hypohidrosis) or do not sweat at all (anhidrosis). But they still experience the CholU rash when their body temperature increases.3

How is CholU diagnosed?

Doctors will often diagnose CholU clinically. That means they will ask about your symptoms and what causes them. Then the doctor will compare your symptoms to those of CholU to see if they match.1

Some doctors may also order a “provocation test.” In this test, you will exercise or sit in a warm bath to increase your body temperature. Then the doctor can see if raising your temperature causes the classic CholU rash. Your doctor may also perform blood tests to determine your CholU subtype.1

How is CholU treated?

The first-line treatment for CholU is a class of drugs called histamine antagonists or antihistamines. These drugs are often used for seasonal allergies. They block the effects of histamine to prevent the CholU rash and other symptoms.1

Because CholU is caused by activation of the immune system, some doctors are interested in trying immune treatments. A small study showed that biologic drugs like omalizumab could significantly improve or completely prevent CholU symptoms. Omalizumab blocks receptors on mast cells. The drug seemed to work better in women.2

More research needs to be done to understand how and when to use such drugs to treat CholU.