August 11, 2023

What Causes Hives (Urticaria)?


Hives (or urticaria) are raised bumps, welts, or blotches on the skin that can be red, pink, or skin-colored and may sting or itch. They are typically an overreaction of the immune system that you can develop because of something you ate or an irritant in the environment. 

What causes hives? What do hives look like? How long do hives last? This article answers these and other questions. 

Why Do You Develop Hives on Your Skin?

Hives typically develop when you ingest or are exposed to something that causes a reaction from your immune system. These irritants include foods, medications, pet dander, pollen, insect bites, etc. 

You may also develop hives due to an infection, stress, wearing tight clothing, heavy sweating, or exposure to temperature extremes. And in many instances, the cause of hives is unknown. 

Whatever the trigger, your body responds by releasing chemicals called histamines into your bloodstream. Histamines help your body fight chemical or biological “invaders” in various ways, including by making you sneeze or itch. They also make it easier for white blood cells to reach the affected site and attach unknown substances. 

What Do Hives Look Like?

Hives can have various forms, including:

  • Small and round
  • Ring-shaped
  • Random-shaped
  • Large, raised areas

Smaller spots grouped together are sometimes called urticaria rash.

Hives can also change their shape, get larger, increase in number, and spread. They may also fuse to form a large, raised area. In some cases, hives look white when you press them. 

What Are the Different Types of Hives (Urticaria)?

Doctors group hives into categories that include:

  • Anaphylaxis. This is a life-threatening allergic reaction that requires immediate medical attention. The hives are often accompanied by trouble breathing, nausea, vomiting, dizziness, and other symptoms. People who know they are at higher risk of anaphylaxis should carry auto-injectors of epinephrine to offset its effects. 
  • Allergic reactions. People allergic to specific substances may develop hives when coming into contact with them. They may take allergy medications to reduce the reaction and avoid their allergy triggers. 
  • Infection-induced hives. Bacteria (from urinary tract infections, strep throat, etc.) and viruses (from colds, mononucleosis, and colds) can cause hives. 
  • Dermatographism. This type of hives is typically mild and results from continuous pressure on the skin, such as from tight clothing. 
  • Temperature-induced hives. Temperature changes or extremes can cause hives in some people. This includes exposure to cold air, cold water, sunshine, or heat.
  • Chronic hives. Hives that recur frequently or persist for weeks or months are considered chronic. They can be very uncomfortable and may indicate an underlying disease like lupus, type 1 diabetes, thyroid disease, rheumatoid arthritis, or celiac disease.

How Long Do Hives Last?

How long hives last depends on several factors, including the cause. Hives from foods or medications often resolve within six hours, while those from infections can last for days. Hives from other or unknown causes may last for minutes or months.

How to Treat Hives

Treatment for hives varies. In many cases, they resolve on their own and require no treatment. In others, over-the-counter antihistamines like Benadryl (diphenhydramine ) reduce or eliminate hives. 

You may also get relief from hives or prevent them by:

  • Taking a lukewarm or cool bath with baking soda or colloidal oatmeal
  • Identifying and avoiding your triggers
  • Avoiding hot water, which can worsen hives

When to See Your Doctor About Urticaria

If you develop hives on your tongue or around your throat or have hives with difficulty breathing, you should seek emergency medical attention or call 911. 

Your Baptist Health primary care physician or an allergy specialist can help if you have recurring hives and want to determine the cause, learn about prevention, or get treatment.

Learn More.