What Causes Unexpected Hives?

Medically Reviewed By Marc Meth, MD, FACAAI, FAAAI
Was this helpful?
189

Possible causes of hives include allergic reactions, certain medications, and infections. Hives can be itchy, alarming, and, in rare cases, life threatening. Most of the time, hives are mild and appear for no apparent reason. Still, there are many identifiable reasons you could break out in hives, and some of them might surprise you.

Read on to learn more about hives, what causes them, and how to treat them.

What are hives?

Young woman scratching back
Lucas Ottone/Stocksy United

Hives, or urticaria, appear when your body releases certain chemicals, including histamine. These chemicals can cause itching, inflammation, and red bumps or patches on your skin.

If your hives last less than 24 hours, finding and avoiding the cause of them might be all you need to do. However, if your hives last longer than 6 weeks and appear for no apparent reason, you may have chronic idiopathic urticaria. The word “chronic” means ongoing, and “idiopathic” means that the cause is unknown.

You should work with your primary healthcare professional to develop a treatment plan that is right for you. You can also work with a specialist, such as a dermatologist or allergist, as another option.

What are the causes of hives?

Many things can trigger hives, such as ingesting a certain food or medication or coming into contact with something that irritates your skin. Certain medical conditions and illnesses can bring on hives as well. Some causes of hives are mild, and some can be more serious.

Common causes of hives

  • Bacterial infections: These can include urinary tract infections and strep throat. If you have a bacterial infection and are on antibiotics, your hives may disappear as your antibiotics start working. 
  • Viral infections: Certain viruses such as colds or infectious mononucleosis can cause hives. In these cases, the hives tend to go away toward the end of the illness. 
  • Vasculitis: This occurs when your blood vessels become inflamed. These hives can be more painful than itchy and can leave behind bruises. You may need a skin biopsy to help diagnose vasculitis. 
  • Stress: Stress and anxiety can occasionally cause you to develop hives. If you are feeling stressed, your body releases chemicals that can trigger itching and inflammation in different areas. 
  • Sunlight: If you have a sun allergy, you can get hives from direct or indirect sunlight exposure. This is known as solar urticaria, and it can occur very shortly after sun exposure. 
  • Pressure: If you wear belts or tight clothing that does not breathe well, they may cause swelling and redness in the area several hours later. These symptoms are known as delayed pressure urticaria.
  • Scratching: Scratching at an area of skin might cause hives that appear within minutes. These hives tend to go away within an hour. This is called dermatographia.
  • Temperature: Changes in temperature, such as being exposed to the cold (cold urticaria) and then quickly warmed up can cause hives. Hot showers or anything that raises body temperature can also be a trigger (cholinergic urticaria). 
  • Certain medical conditions: Hives can come and go with some medical conditions, such as type 1 diabetes, thyroid conditions, lupus, and rheumatoid arthritis.

Potentially serious causes of hives

  • Food allergies: Some common foods that can cause allergic reactions include nuts, milk, eggs, sesame, and seafood. These reactions can sometimes be severe and cause anaphylaxis, a serious condition requiring immediate medical treatment. Anaphylaxis can cause chest tightness, hives, difficulty breathing, vomiting, and rapid heartbeat. 
  • Medication allergies: Antibiotics such as penicillin and sulfa drugs can cause hives, itching, wheezing, and swelling. Other common medications that can cause allergies include aspirin and ibuprofen. If the allergy is severe, it can cause anaphylaxis. 
  • Insect stings or bites: Insect bites can cause itching and bumps on your skin. Some stings, such as bee stings, can cause an allergic reaction that can be more serious. If you are allergic to bee venom, you may need to carry an epinephrine pen. An epinephrine pen can help decrease your symptoms if you are stung and potentially avoid an anaphylactic reaction.
  • Blood transfusions: Receiving a blood transfusion can trigger an allergic reaction. If this happens, you may break out in itchy hives along with an elevated temperature, chills, and trouble breathing.

What do hives look like?

Hives, or urticaria, refers to a rash that causes temporary raised, itchy welts on the skin.

Allergy skin back and sides. Allergic reactions on the skin in the form of swelling and redness
Panther Media GmbH/Alamy Stock Photo

Hives refers to a raised, itchy rash that can occur due to a reaction to many different stimuli. The most common causes are allergic reactions, drug reactions, and stress.

hives-2-1024x575.jpg
Created by Samuel Freire da Silva, M.D. in homage to The Master And Professor Delso Bringel Calheiros. Image obtained from Dermatology Atlas

Hives is often due to an allergy to things in your environment or a reaction to a medication. This raised, itchy rash usually resolves with time and does not typically require further evaluation.

Women scratch the itch with hand
dtephoto/Getty Images

Hives causes a raised, itchy rash to form. It can occur on any area of the skin.

woman showing her skin itching behind , with allergy rash urticaria symptoms
chokja/Getty Images

When should I see a doctor for hives?

Some reasons to call your doctor include:

  • swelling under the skin
  • hives that spread quickly
  • feeling ill with a high temperature
  • symptoms that last more than 2 days

Seek immediate medical care if your hives are accompanied by:

  • swelling on your face, in your throat, or in your mouth
  • trouble breathing
  • wheezing
  • chest or throat tightness

What are some treatments and home remedies for hives?

Not all hives have an obvious cause, and you might live with hives for months or years without knowing why. Whether you know the cause of your hives or not, different treatment options are available. 

Medications

  • Antihistamines: Allergy medications such as cetirizine (Zyrtec), diphenhydramine (Benadryl), fexofenadine (Allegra), or loratadine (Claritin) can help treat hives. Antihistamines are the most common medication type for treating hives. Prescription antihistamines might be necessary if over-the-counter medications are not working.
  • Corticosteroids: If antihistamines are not working or your hives are severe, your healthcare professional might recommend a short course of a corticosteroid, such as prednisone. However, courses of corticosteroids should be limited due to their potential for side effects.
  • Monoclonal antibody treatment: Omalizumab (Xolair) is a medication for people with chronic urticaria that has been approved by the Food and Drug Administration. Doctors will often prescribe this medication if antihistamines are not working and the hives are severe.
  • Leukotriene modifiers: These medications work by blocking the substances that produce inflammation. The most common leukotriene modifier is montelukast (Singulair). 

Home remedies

In addition to medications, you can also try some things at home to reduce your symptoms:

  • Avoid using hot water on the affected area. Heat can worsen hives. 
  • Take lukewarm or cool baths with baking soda or colloidal oatmeal to help protect the skin and reduce itching and inflammation.
  • Use cold compresses on the affected area for 10 minutes at a time. 
  • Wear lightweight clothing and keep your home cool. Use light bedding if you find you are breaking out in hives when you sleep. 
  • Use unscented soaps or lotions for sensitive skin.

Frequently asked questions

What does it mean when you get hives out of nowhere?

Allergic reactions often cause hives, but hives can also happen in other circumstances. Anxiety, stress, exercise, infections, and even tight clothing can cause hives. Often, people break out in hives for no apparent reason. Unless you are experiencing a severe allergic reaction, hives are usually mild. 

Can hives be caused by nothing?

According to the American Osteopathic College of Dermatology, about 95% of the time, doctors cannot find a reason that recurring hives appear. However, it is still important to see a doctor or specialist for treatment. 

What should I do if I randomly break out in hives?

If you break out in hives for no apparent reason, inform your doctor. They may want to do testing. It is important to try to figure out the cause of your hives to help you avoid triggers in the future.

Summary

Common causes of hives can include allergies, medications, and infections. Treatment for hives usually includes medications like antishistamines or corticosteroids, but some home remedies may help as well.

Talk to your doctor about possible causes for your hives. If you are experiencing serious symptoms like vomiting or difficulty breathing, seek medical care immediately.

Was this helpful?
189
Medical Reviewer: Marc Meth, MD, FACAAI, FAAAI
Last Review Date: 2022 Mar 29
View All Allergies Articles
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Alkeraye, S., et al. (2021). The addition of montelukast for the treatment of chronic idiopathic urticaria. https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC8327886/
  2. Bernstein, J. A., et al. (2020). Benralizumab for chronic spontaneous urticaria. https://www.nejm.org/doi/full/10.1056/NEJMc2016395
  3. Drug allergies. (2018). https://acaai.org/allergies/allergic-conditions/drug-allergies/
  4. Food allergies. (2022). https://www.fda.gov/food/food-labeling-nutrition/food-allergies
  5. Hives. (2018). https://acaai.org/allergies/allergic-conditions/skin-allergy/hives/
  6. Hives. (2021). https://www.nhs.uk/conditions/hives/
  7. Kanani, A., et al. (2018). Urticaria and angioedema. https://aacijournal.biomedcentral.com/articles/10.1186/s13223-018-0288-z
  8. Lesiak, A., et al. (2018). Omalizumab for urticaria treatment in clinical practice: A case series. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6130138/
  9. Ludmann, P. (2021). Hives. https://www.aad.org/public/diseases/a-z/hives-overview
  10. Son, J. H., et al. (2018). A histamine-free diet is helpful for treatment of adult patients with chronic spontaneous urticaria. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5839887/
  11. Suddock, J. T., et al. (2021). Transfusion reactions. https://www.ncbi.nlm.nih.gov/books/NBK482202/
  12. Urticaria. (n.d.). https://www.aocd.org/page/Urticaria