Cholinergic urticaria is a type of skin rash commonly called hives that occurs in some people when their body gets too warm and sweats. The rash usually develops very quickly after a person gets too hot.

In most cases, the condition clears up quickly on its own with no real lasting effects. However, some people may find cholinergic urticaria adversely affects their ability to exercise.

Rarely, people with cholinergic urticaria may experience severe reactions to heat that result in a life-threatening allergic reaction.

The word “cholinergic” refers to a part of the nervous system that controls muscle contraction, dilation of the blood vessels, and slowing the heart rate.

In this article, we examine the signs and symptoms of cholinergic urticaria, along with what can be done to treat it. We also take a look at what can cause cholinergic urticaria and how people can prevent it.

An arm with a dotted rash resembling cholinergic urticaria.Share on Pinterest
Cholinergic urticaria is a skin rash that can develop if a person gets too hot.
Image Credit: PKeMcG, 4 December 2012

Cholinergic urticaria tends to occur very quickly after a person begins to sweat or gets overheated.

The rash can occur anywhere on a person’s body but may be more likely to appear on a person’s trunk or arms.

Typical signs and symptoms of the rash include any combination of the following:

  • itching or tingling at the onset of the rash
  • burning or itching in areas affected by the rash
  • areas of smaller weals, which are red, raised bumps on the skin
  • larger weals that lead to more significant areas of swelling

Most of the time, cholinergic urticaria is not serious, and the rash will fade on its own within an hour of its appearance.

Possible complications

Some people may have more severe reactions to cholinergic urticaria, however. A person who experiences a severe reaction may develop symptoms elsewhere in their body, including:

In some instances, people with severe reactions to cholinergic urticaria may develop anaphylaxis, a life-threatening allergic reaction that requires emergency medical attention.

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The heat from saunas could trigger cholinergic urticaria.

Cholinergic urticaria may occur any time a person sweats or gets too warm. The following events or situations can cause a person to develop cholinergic urticaria:

  • exercise
  • hot baths
  • sitting in a sauna or hot tub
  • being in a warm room
  • exposure to hot weather
  • running a fever
  • being angry or upset
  • stress
  • eating spicy food

Scientists believe these situations raise a person’s body temperature and cause the body to release histamine, a compound that the body tends to release in response to injury. This compound triggers some people to develop cholinergic urticaria.

When symptoms of cholinergic urticaria occur and are disruptive but not severe, a doctor can likely diagnose the condition from a description of the person’s symptoms.

A doctor may want to run tests to confirm the diagnosis of cholinergic urticaria, however. These tests may include:

  • An exercise challenge: while a person is exercising, the doctor will monitor them for signs of cholinergic urticaria.
  • A passive warming test: a person will sit in a warm room or warm water while a doctor checks the skin for signs of cholinergic urticaria.
  • A methacholine skin challenge test: a doctor injects a drug called methacholine into a person’s skin to see if cholinergic urticaria develops.

Treatment options vary from person to person and may range from medications to lifestyle changes, such as avoiding triggers. Some people, such as athletes, may not be able to avoid exercise so a doctor may recommend medical management right away.

Doctors may suggest antihistamine medication, such as H1 agonists, or anticholinergic drugs to treat this condition.

At present, however, there is no single way to treat cholinergic urticaria that is deemed to be completely effective.

For people who manage the condition through lifestyle changes, avoiding triggers is usually the best approach. People looking to avoid triggers for cholinergic urticaria should avoid the following:

  • exercise
  • spicy food
  • hot showers and baths
  • prolonged exposure to heat

Also, people looking for lifestyle management should look for ways to reduce and manage their stress and anger, such as through meditation or journaling.

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A low-histamine diet, which would include avoiding fish and shellfish, may help chronic urticaria.

Some specialists recommend people adopt a low-histamine diet to help with chronic urticaria. Histamine is a chemical involved in the body’s allergic response.

The theory behind a low-histamine diet is that reducing foods that contain histamine will help the body absorb less histamine. Absorbing less histamine would then reduce the allergic response causing the urticaria.

People on a low histamine diet should reduce or avoid foods such as:

  • salty foods
  • fish and shellfish
  • foods high in preservatives or additives
  • nuts
  • vinegar
  • dairy
  • alcohol
  • many fruits and vegetables

Another diet option is an elimination diet. An elimination diet is designed to help a person find out which foods might trigger an allergic response. Introducing foods into the diet and then eliminating any that might trigger an allergic reaction can help prevent or reduce the severity of any cholinergic urticaria reactions.

It is important to note that diets are not well-studied for their effectiveness in actually reducing symptoms of cholinergic urticaria.

Anyone planning a restrictive diet should discuss it with a doctor or dietitian, especially if they have other health conditions.

One of the simplest ways to prevent cholinergic urticaria is avoiding trigger activities. People who experience cholinergic urticaria should avoid exercises that cause excessive sweating or heat.

Similarly, they should also avoid situations or activities that make a person hot. This is particularly true during summer months.

A doctor will likely prescribe antihistamines to help prevent allergic reactions. These medications will help prevent a person’s body overreacting to triggers. Other medication options include:

For those who experience anaphylaxis during exercise, a doctor will likely prescribe an EpiPen. A person will also likely want to find a workout partner to help in case of an emergency.

Mostly, symptoms disappear a few hours after they first appear. People who experience frequent or long-lasting symptoms may wish to speak to their doctor about better ways to prevent the condition.

If a person experiences any trouble breathing during exercise, they should seek immediate medical attention.