They're caused by nerve fibers in your sweat glands. Your skin reacts to the heat and sweat when your body temperature goes up.
You may get these hives when you:
- Take a hot shower or bath
- Work up a sweat from exercise
- Are in a hot climate
- Wear a tight, clingy bandage
- Get nervous and start to sweat
- Eat hot or spicy foods
Some people may get them if their body has an autoimmune response to an antibody in their own sweat called immunoglobulin-G (IgG). Elevated levels of IgG are found in people with chronic autoimmune urticaria.
You may be more likely to get these hives if you have eczema, asthma, or other allergies like hay fever, or if you get hives for other reasons, such as from certain foods or medications, pressure on your skin, or cold weather. Both men and women can get cholinergic urticaria.
These hives are itchy, tingly, and warm. They're usually small red bumps with flares or circles around them called wheals.
You can get them anywhere on your body, but most of the time they show up on your chest, face, upper back, and arms. Sometimes, the bumps are close together. Your skin can look swollen and blotchy, or you may just look flushed.
CU hives pop up within 6 minutes of contact with a trigger. They last about 30 minutes to an hour or two before they fade away.
It's not common, but you also may have one or more of these along with hives:
- Extra saliva in your mouth
- Low blood pressure
- Rapid heartbeat
- Shortness of breath
- Stomach cramps
If you notice that your skin gets itchy, red, and blotchy when you're hot or you're a few minutes into a workout, see your doctor. A dermatologist (skin specialist) or allergist can also diagnose CU.
Your doctor will ask you what your hives look like when you get them and how long they last to rule out other causes, such as foods you eat. Your doctor may ask you to run or ride a stationary bike for about 15 minutes to see if you break out as you sweat.
A shot of methacholine, a medicine that shrinks your airways, may also be used to make the bumps show up.
If you live in a hot climate or like to exercise, it can be hard to stay away from the heat that causes these hives.
- Cetirizine (Zyrtec)
- Diphenhydramine (Benadryl)
- Hydroxyzine (Atarax, Vistaril)
- Fexofenadine (Allegra)
- Loratadine (Alavert, Claritin)
If antihistamines don't work, your doctor may recommend steroids for a short time or histamine 2 receptor blockers such as Zantac or Tagamet. All antihistamines are more effective if taken daily rather than on an as-needed basis.
Other treaments for CU include leukotriene inhibitors (Singulair), immunosuppressives (cyclosporine, dapsone), Danazol, beta-blockers (propranolol), topical scopolamine, and omalizumab (Xolair).
If you have serious reactions -- like shortness of breath -- when you get hives, he may prescribe an epinephrine shot for you to keep on hand. This can help your breathing and get rid of hives and swelling.
Stop or slow down your workouts if you break out in hives. If some types of exercise make you break out more often, try other activities instead.
Cool your hot skin to prevent or ease hives:
- Try a cool shower, press a cloth soaked in cool water to your skin, or stand in front of a fan.
- Wear loose clothes.
- Keep your home and bedroom at a cool temperature.
- If stress causes your hives, try to avoid situations that upset you. Find ways to calm down and manage it.