Hives: Itchy Welts, Common Triggers and When to Call 911

What it involves

MedlinePlus describes hives as raised, usually itchy, red bumps or welts on the surface of the skin. They can be an allergic reaction to a food or medicine, or can appear without any cause. When you react to a substance, the body releases histamine and other chemicals into the blood, which causes the itching and swelling.

Who this is for

• Patients with itchy raised welts that keep coming back, move around, or fade and reappear within hours
• Patients whose hives have lasted more than a few weeks
• Patients who wonder if a food, medicine, or insect bite set them off
• Patients who want a plan for what to do if swelling ever involves the face or throat

What to expect

• Questions about when the welts started, how long each one lasts, and recent foods, medicines, or illnesses
• A look at the skin, since hives are usually diagnosed by how they appear
• A plain plan that often starts with an antihistamine and trigger avoidance
• A referral to an allergist if the pattern points to a specific allergy

What hives look like

MedlinePlus says hives are swollen, red or skin-colored welts, called wheals, with clearly defined edges. They may get bigger, spread, and join together, and they often change shape, disappear, and reappear within minutes or hours. It is unusual for a single wheal to last more than 48 hours. Dermatographism, or skin writing, is a type caused by pressure or scratching that raises welts right where the skin was touched.

Common triggers

MedlinePlus lists many substances that can trigger hives:

• Animal dander, especially from cats, and pollen
• Insect bites and certain medicines
• Foods such as shellfish, fish, nuts, eggs, and milk
• Emotional stress, extreme cold or sun, exercise, and excessive sweating
• Infections such as mononucleosis, and illnesses such as lupus

Often the cause is never found

MedlinePlus says that often the cause of hives is not known. When it is, it may be a food or medicine, and allergy testing is not useful in most cases of hives. It says a provider can usually tell by looking at the skin, and that a skin biopsy or blood tests are only sometimes done to confirm an allergic reaction. If a bite set it off, the insect bites and stings guide covers that route.

What helps

MedlinePlus says mild hives may need no treatment and may disappear on their own. To reduce itching and swelling it suggests avoiding hot baths and showers and tight-fitting clothing. A provider may suggest an antihistamine, and other prescription medicines may be needed if the hives are long-lasting. Hives that look like a general rash are one of the patterns sorted in the skin conditions guide, and itchy eyes and sneezing alongside suggest allergy, covered in the seasonal allergies guide.

Call 911 for these signs

MedlinePlus says to call 911 if hives come with fainting, shortness of breath, tightness in the throat, tongue or face swelling, or wheezing. Angioedema, swelling of the deeper tissue that sometimes occurs with hives, can block the airway when it is around the mouth or throat. A severe reaction may need an emergency shot of epinephrine, which is given in an emergency setting, not at a routine visit.

How long hives last

MedlinePlus says hives are uncomfortable but usually harmless and disappear on their own. When they last longer than 6 weeks they are called chronic hives, where usually no cause can be found, and most chronic hives resolve on their own in less than a year. It advises contacting your provider if hives are severe, uncomfortable, and do not respond to self-care, and avoiding exposure to anything that has triggered them before.

Sources

• MedlinePlus — Hives
• MedlinePlus — Hives health topic