Hives are a skin reaction of itchy bumps that may burn or sting. They can develop not only from an immune response to an allergen but also to heat.
While you may think of hives or urticaria as resulting from an allergic reaction, they can also be caused by heat. These are called heat hives or cholinergic urticaria.
In some people, a rise in temperature can produce the chemical histamine, similar to what happens when your immune system fights allergies. Histamine dilates blood vessels and results in swelling.
There is limited research on cholinergic urticaria. The few available studies estimate a wide prevalence range of
If you notice hives tend to break out when your body temperature rises, it may be a sign that heat triggers your hives. Any exposure to heat could potentially trigger heat hives. This can include:
- bathing in warm or hot water
- being near a heat source like a stove
- being outdoors in the sun
- eating hot food
According to research from 2022, physical factors that can contribute to the development of heat hives include:
- being allergic to sweat
- clogged sweat ducts, lack of sweating
- medications or substances that affect the neurotransmitter acetylcholine
Although being allergic to sweat is rare, research shows that 66% of patients who get heat hives also have a histamine response against antigens in their sweat.
In rare cases, heat hives
Get step-by-step instructions on how to use an EpiPen.
Heat rash vs. hives
Heat hives share similar causes and symptoms with many forms of heat rash, also known as miliaria.
Heat rash can also be
While heat rash tends to fade on its own, consider visiting your doctor for more severe or persistent cases. Your doctor can provide a proper diagnosis and help you determine whether you’re experiencing hives or heat rash.
The symptoms of heat hives are similar to hives caused by other triggers such as insect bites, allergies, or medications.
Hives can appear as red, itchy welts ranging in size from less than half an inch up to several inches in diameter. Hives on darker skin tones may appear closer to the color of the skin.
Most cases of hives caused by heat appear within a few minutes after exposure and will subside within 1-2 hours. However, heat hives can also be accompanied by angioedema, which is swelling beneath the affected skin caused by leaking blood vessels.
In some cases, you can also experience other symptoms along with heat hives. These include:
- fatigue or weakness.
You may be experiencing exercise-induced anaphylaxis if you also have the following symptoms:
- difficulty breathing
- abdominal pain
Call 911 if you experience these symptoms. If you have an EpiPen, you should administer the medication while you wait for help to arrive.
Anaphylaxis is a severe reaction to a trigger, such as an allergy, and is potentially life threatening.
Symptoms can come on quickly and include:
- feeling faint or lightheaded
- difficulty breathing or wheezing
- rapid heartbeat
- clammy skin
- collapsing or losing consciousness
- stomach pain, nausea, or vomiting
If you or someone around you develops these symptoms, you should:
- Check to see whether they have an epinephrine pen. If they do, read and follow the instructions to dispense the medication.
- Dial 911 (or a local emergency number).
- Lay them down. If they have vomited, lay them on their side.
- Stay with them until emergency services arrive.
It is possible for someone to need more than one injection with an epinephrine pen. If symptoms do not begin to clear after 5 minutes, give a second injection if one is available.
If your symptoms aren’t severe but interfere with your lifestyle, see your doctor. A simple evaluation and conversation about your symptoms may be enough for them to diagnose heat hives.
Sometimes, your doctor may want to conduct tests to gather more information about the condition. These may include:
- A passive warming test: This will raise your body temperature with warm water or an increased room temperature. Your doctor can observe your body’s reaction when exposed to increased heat.
- A methacholine skin challenge test: Your doctor may inject a medication called methacholine into your body and observe for a reaction. However, not everyone with heat hives gets a positive result, so the doctor may use this test in combination with others.
- An exercise challenge test: Your doctor will have you exercise and watch for symptoms of CU. You may also be measured with other medical instruments during the test.
You should see a doctor immediately if you suspect you have exercise-induced anaphylaxis, which must be attended to as soon as symptoms occur.
Many cases of heat hives fade on their own in a few hours, but certain home remedies, prescription medications, and prevention techniques can ease symptoms and alleviate flare-ups.
Home remedies you can try include aloe vera, which has known anti-itching properties, or a colloidal oatmeal bath, which
But prior to topical applications of this sort, remember to check the ingredients to ensure that you aren’t allergic to any of them.
You can also take a few precautions to help prevent heat hives:
- Try to keep cool while exercising.
- Prevent exposure to areas of high humidity.
- Avoid prolonged periods of direct sunlight exposure.
If such home remedies don’t work, your doctor may recommend beginning taking an antihistamine such as:
- H1 antihistamines such as citirizine (Zyrtec, Aller-Tec, and Alleroff) or loratadine (Claritin)
- H2 antihistamines (H2 blockers or antagonists) such as famotidine (Pepcid, Pepcid AC) or cimetidine (Tagamet, Tagamet HB)
If these medications don’t relieve the symptoms sufficiently, your doctor
- systemic drugs like methotrexate or dapsone (Aczone)
- biologics like omalizumab (Xolair)
- leukotriene receptor antagonists such as montelukast
In some cases, your doctor may prescribe a medication off-label. One example of such medication is dupilumab (Dupixent), which is another biologic medication that
Most instances of heat hives can be treated at home and eventually fade on their own. However, you should seek immediate medical attention if swelling occurs in your throat that makes it difficult to breathe. This can be a sign of a serious allergic reaction and anaphylaxis.
You and your doctor can work to identify the specific triggers of your heat hives and develop a prevention plan with ways to ease symptoms if flare-ups do occur.