What Causes Hives? Common Triggers, Underlying Causes and Why Many Cases Have None
Hives happen when your skin releases histamine and other chemicals that make fluid leak from tiny blood vessels, but what sets that process off differs from person to person. Sometimes the cause is easy to spot, like a new medicine or an insect sting. Often it is not. This guide covers the most common causes of hives, how to look for your own triggers, and why finding no cause is so common.
How Hives Form
In the skin, mast cells store histamine. When something activates them, they release it, causing swelling (the welt) and itching. The triggers fall into a few broad groups, outlined below.
Common Causes of Hives
Infections
Infections are among the most frequent causes of short-term hives, especially in children. Viral illnesses such as colds and the flu are the most common culprits, and bacterial infections such as strep throat and urinary tract infections can also trigger them. Hives from an infection usually clear as the illness passes.
Foods
Foods that commonly trigger hives include shellfish, fish, eggs, milk, tree nuts, peanuts, wheat and soy. Food-triggered hives typically appear within minutes to a couple of hours after eating. See food allergy hives.
Medications
Medicines known to cause hives include aspirin and other NSAIDs (such as ibuprofen and naproxen), antibiotics (especially penicillins and sulfa drugs), ACE inhibitors, and opioid pain relievers such as codeine. If hives started soon after you began a new medicine, tell your doctor before you stop taking it.
Insect stings and bites
Stings from bees, wasps and fire ants can cause hives, sometimes as part of a wider allergic reaction.
Contact with substances
Touching latex, certain plants, animal saliva or dander, or some cosmetics and cleaning products can cause hives where the skin made contact.
Physical triggers
Some hives are brought on by something that affects the skin directly: cold, heat, sunlight, pressure, vibration, water, sweating, exercise or scratching. These are called inducible or physical hives. Learn more about the different types of hives.
Stress
Emotional stress does not cause every case, but it can trigger or worsen hives in some people. Read more about stress hives.
Autoimmune and other health conditions
Chronic hives are sometimes linked with autoimmune conditions, especially thyroid autoimmunity, and less often with lupus and other disorders. In rare cases, long-lasting hives are associated with other underlying illnesses, which is part of why a doctor evaluates persistent hives. Learn about autoimmune hives.
Hives With No Known Cause
In most people with chronic hives, no outside trigger can be found. Doctors call these hives chronic spontaneous or idiopathic urticaria. It can be frustrating, but it does not mean something is being missed or that treatment will not work. Hives from allergic reactions are a minority of cases. See allergic reaction hives for how to tell.
Causes of Hives in Adults
In adults, hives are more often chronic and more often have no identifiable trigger, and are more common in women. Stress, medications, infections and autoimmune factors are commonly considered. See causes of hives in adults.
How to Find Your Triggers
- Keep a diary. Record when hives appear, what you ate, which medicines you took, what you did and how you felt beforehand.
- Look for patterns. If hives always follow the same activity, food or exposure, that is a clue.
- Avoid suspected triggers on a trial basis, ideally with a doctor’s guidance, especially before cutting out whole food groups.
- Ask about testing. Allergy testing is useful when a specific food, medicine or sting is suspected, but is rarely helpful otherwise.
When Hives Are an Emergency
Treat these symptoms as an emergency and call 911 if hives appear together with shortness of breath, a hoarse voice or trouble swallowing, swelling of the face, tongue or throat, a racing heartbeat, fainting, or vomiting and severe stomach cramps soon after a food, medication or insect sting. Do not wait to see whether they pass.
When to See a Doctor
See a doctor if your hives last more than a few days, keep returning, or reach the 6-week mark. Dr. Tiffany Young’s Hives Treatment Center in San Francisco is a practice dedicated to diagnosing and treating hives, and offers both online and in-person consultations.
Frequently Asked Questions About the Causes of Hives
What is the most common cause of hives?
For short-term hives, infections (especially viral) are among the most common. For chronic hives, there is often no identifiable cause.
Can hives be caused by stress?
Stress can trigger or worsen hives in some people.
Are hives always an allergic reaction?
No. Allergies are one possible cause, but many hives come from infections, physical triggers or unknown causes.
Can you be allergic to the cold or sun?
Strictly speaking these are not typical allergies, but cold and sunlight can trigger hives in some people.
Treat Hives Whatever the Cause
Even when the cause stays unknown, hives can be controlled. Visit our hives treatment page to see the latest treatment options for your outbreak.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. If you think you are having a medical emergency, call 911.
