What causes hives?
Hives are often-itchy bumps and raised patches that develop when the body releases histamine.
Your body stores histamine inside cells. When your immune system recognizes a threat, it releases histamine and other chemicals. This cascade of chemicals can protect you from becoming seriously ill from an infection, spoiled fish, or a bug bite.
Sometimes, the immune system releases histamine when there is no real threat. This happens when people develop an allergic reaction. In fact, some people develop hives when they have an allergic reaction.
Some people develop hives when they have an allergic reaction
The hives on this boy’s skin are due to an allergic reaction to mosquito bites.
When the body mistakenly releases histamine and hives develop, the cause is often one of the following:
An allergic reaction
Overreaction to heat, sweat, or cold
Pressure on the skin (tight clothing, light touch of a purse strap, or scratching)
When hives are due to an allergic reaction, it’s often an allergy to:
Bug bite or sting
Infection or medical treatment can trigger hives
Some people get hives when they develop an infection like strep throat, a urinary tract infection, or COVID-19.
Others get hives when they have a medical treatment like radiation therapy or a blood transfusion.
Hives was the first sign of COVID-19 for this girl
A few days after getting hives, this 5-year-old girl began to develop the more common symptoms of COVID-19 like fever and a cough.
Hives due to radiation therapy
This medical treatment can be lifesaving but hard on your skin. If your body releases histamine to protect itself, hives can develop.
What triggers hives often remains a mystery
While some people can trace hives back to a trigger like an allergic reaction, exposure to cold, or stress, the cause remains a mystery for many people.
It’s estimated that millions of people in the United States will develop hives during their lifetime and never find the cause. Some of these people will continue to have hives for six weeks or longer. When this happens, the person has a medical condition called chronic spontaneous urticaria (CSU).
Urticaria is the medical word for hives.
With CSU, hives can continue to appear for months and sometimes years. During this time, the swelling, pain, and discomfort can be difficult to live with.
Women are twice as likely as men to develop CSU during their lifetime. Most women develop CSU when they are 20 to 40 years of age.
Some people have greater risk of developing any type of hives
While anyone can develop hives, you have a greater risk if you:
Are a woman of African American heritage (4 to 5 times greater risk than white people)
Have atopic dermatitis (eczema)
If you have long-lasting or widespread hives, seeing a dermatologist can help you feel more comfortable. Seeing a dermatologist is also a good idea to make sure that what you have really is hives.
Find out how dermatologists diagnose and treat hives at: Hives: Diagnosis and treatment.
Related AAD resources
Image 1: Used with permission of the American Academy of Dermatology National Library of Dermatologic Teaching Slides.
Image 2: Images used with permission of JAAD Case Reports.
JAAD Case Reports 2021;11:137-8.
Image 3. Image used with permission of the Journal of the American Academy of Dermatology.
J Am Acad Dermatol 2006;54(1)28-46.
Antia C, Baquerizo K, et al. “Urticaria: A comprehensive review: Epidemiology, diagnosis, and work-up.” J Am Acad Dermatol. 2018;79(4):599-614.
Grattan CEH, Saini SS. “Urticaria and angioedema.” In: Bolognia JL, et al. Dermatology. (4th edition). Mosby Elsevier, China, 2018:304-19.
Hide M, Takahagi S, et al. “Urticaria and angioedema.” In: Kang S, et al. Fitzpatrick’s Dermatology. (9th edition) McGraw Hill Education, United States of America, 2019:684-785.
Hymes SR, Strom EA, et al. “Radiation dermatitis: Clinical presentation, pathophysiology, and treatment.” 2006. J Am Acad Dermatol. 2006;54(1):28-46.
Le NK, Brooks JP. “Acute urticaria as the initial presentation of COVID-19 in a pediatric patient.” JAAD Case Rep. 2021;11:137-8.
Rosman Y, Hershko AY, et al. “Characterization of chronic urticaria and associated conditions in a large population of adolescents.” J Am Acad Dermatol. 2019;81(1):129-135.
Paula Ludmann, MS
Rajiv Nijhawan, MD, FAAD
Dara Spearman, MD, FAAD
Last updated: 9/28/21