Cholinergic Urticaria (aka CU) is a lesser known but not uncommon form of hives. It’s characterized by small, intensely itchy bumps that appear on the skin in response to an increase in body temperature.
Unlike other types of hives there are no allergic triggers such as foods, medications, or environmental factors. It is therefore considered as a type of physical urticaria (similar to chronic idiopathic urticaria), rather than a classic allergic reaction. Cholinergic Urticaria is specifically triggered by activities that elevate the body’s temperature. This can include exercise, hot showers, spicy foods, or even emotional stress.
Why do we call it “cholinergic” urticaria?
The term “cholinergic” refers to the role of “acetylcholine” in the aetiology of the itchy rash. Acetylcholine is a neurotransmitter involved in sweating and regulating body temperature. In CU, the release of acetylcholine during heat-induced sweating is what can lead to the development of hives in susceptible individuals.
Causes and Triggers
If we take a look at the underlying causes, we can better understand it, manage it and prevent it from affecting us. Despite various studies, the exact mechanism for acetylcholine causing the hives is not fully understood. Here are the most common factors:
| Cause/Trigger | Description |
|---|---|
| Heat and Exercise | Physical activities that raise the body’s temperature, such as vigorous exercise or walking in heat. |
| Emotional Stress | Stress and anxiety can increase body temperature and lead to sweating, triggering CU. |
| Spicy Foods and Hot Beverages | Consuming items that cause internal warming can precipitate hives. |
| Hot Showers or Baths | Exposure to hot water can raise body temperature and induce sweating. |
| Environmental Heat | Being in a hot climate or experiencing a sudden temperature change can trigger CU. |
| Clothing | Wearing tight or non-breathable clothing can trap heat and sweat, increasing the likelihood of hives. |
The common theme in the above triggers is an increase in body temperature.
For example, you may have noticed that when you’re out running and wearing synthetic clothing, you may get a very itchy area of the skin. This is likely due to a combination of body temperature increase and the clothing trapping the excess heat and sweat.
So what are the symptoms of cholinergic urticaria?
These can vary, ranging from mild itchiness and skin irritation to a more severe and extensive burning sensation.
Small, Red Bumps: Typically ranging from 1-3 millimeters in diameter, these bumps may appear in clusters.
Intense Itching: The affected areas can be extremely itchy, leading to discomfort and sometimes scratching.
Burning Sensation: Some individuals experience a burning or prickling feeling in addition to itching.
Localized Distribution: Hives often appear on the neck, chest, arms, and upper body, areas more prone to sweating. If any of these areas are in contact with clothing that traps moisture and heat, then this specific area will be the most affected.
Short Duration: Unlike other forms of urticaria that can last for hours or days, CU hives usually subside within 24 hours or even quicker in some instances.
How is it diagnosed?
Diagnosis can be tricky and mostly relies on symptoms, signs and exclusion of other more serious causes for the hives and itchiness. The condition can closely resemble other types of urticaria, making accurate diagnosis crucial for effective management
Provocation Tests
Following a detailed history and clinical examination (detailed photos help!), it may be possible to try and provoke this type of urticaria in a controlled environment. Under medical supervision, you can be exposed to heat or undertake exercise to trigger the reaction. This test helps to confirm that the symptoms are directly linked to an increase in body temperature or sweat.
Exclusion of other causes
To exclude other causes of hives, such as allergic reactions to foods, medications, or environmental factors, IgE blood tests or skin prick tests may be required. Allergy testing is important to ensure that your diagnosis is accurate and treatment plan is appropriately targeted to CU and not other allergic conditions.
Treatment and Management Options
Antihistamines
Antihistamines are the first line treatment for cholinergic urticaria. Most patients find that the symptoms improve in the first 24 hours or even quicker after using antihistamines. There are various options for use in the UK, specifically Fexofenadine (Allevia), Cetirizine and Loratadine that can all be bought over the counter.
Identify and Avoid Triggers
Keeping a symptom diary can be vital in understanding what the underlying triggers are. If possible, your allergist may suggest adjusting exercise routines to cooler parts of the day or opting for low-intensity workouts. This can reduce the risk of hives.
If the hives are taught to be worsened by your clothing, then you may want to try different types of clothing that is more breathable.
Keep Cool and Hydrated
Keeping the body cool through air conditioning, cool showers, or cooling garments can help manage symptoms. Staying well-hydrated by drinking plenty of water and electrolytes also aids in regulating body temperature.
Topic Treatments
Depending on how much of the skin is affected, topical treatments may also be an option. Calamine lotion or short courses of topical steroids may be recommended for temporary relief from itching.
Omalizumab
Omalizumab has also been briefly studied in patients with more severe cases of cholinergic urticaria. It has been shown to have a positive impact, particularly in cases of recurrent CU that has not responded to other interventions.
When to Seek Medical Attention
Although cholinergic urticaria is generally manageable, certain situations warrant immediate medical attention:
Difficulty Breathing: If hives are accompanied by wheezing, shortness of breath, or swelling of the throat, seek emergency medical care as these may be signs of a severe allergic reaction (anaphylaxis).
Persistent Symptoms: If hives do not respond to over-the-counter treatments or are affecting your quality of life, consult your GP or an allergist.
Unusual Symptoms: Any new or unusual symptoms accompanying hives should be evaluated to rule out other health conditions.
Prognosis of Cholinergic Urticaria
Cholinergic urticaria can be a chronic condition that can have a high psychosocial impact. With an early diagnosis and effective management strategies, individuals can control symptoms and minimize their impact on daily life. The severity and frequency of hives can vary, with some people experiencing occasional flare-ups and others facing more persistent symptoms.
Natural Resolution
In some cases, CU may improve or resolve over time, especially with age. However, many individuals continue to manage their symptoms successfully with a combination of conservative (lifestyle modifications) and medical treatments.
Impact on Quality of Life: While CU can be uncomfortable and occasionally debilitating, proactive management can enable individuals to maintain an active and fulfilling lifestyle.
If you think you may be suffering from chronic urticaria it’s important to speak to your GP or contact your local allergist so they can look into this further.
