Frequently Asked Questions

Find answers to some of the most common questions about CSU.1

Man researching CSU on laptop

Are CSU and chronic idiopathic urticaria (CIU) the same condition?

Yes, both refer to the same condition – hives that last for six weeks or longer without a known cause. Originally, the condition was called CIU. As medical researchers learned more about it, they began to use CSU more frequently to emphasize the spontaneous nature of the condition. The term CIU was previously used more in the United States and Canada, whereas in other parts of the world doctors may use the term CSU more frequently.

What causes chronic spontaneous urticaria (CSU)?

There is no known cause of CSU. It’s often diagnosed by ruling out other conditions that could cause hives. Even if you can identify things that make your hives worse, CSU is diagnosed by your doctor when no exact cause of your hives can be determined.

What are hives?

Hives are a skin condition that occurs when the body reacts to a substance called histamine or other substances in the blood. This reaction causes raised, red and itchy round bumps on the skin called wheals. The wheals can change, move, merge, grow, appear and disappear on the skin.

Why should I speak with an allergist about my CSU?

If you suspect you have CSU, make an appointment with an allergist. Allergists are trained to diagnose immune system conditions such as allergies and asthma, and they have special training in diagnosing hives. An allergist will be able to offer the appropriate tests you will need to rule out other conditions that could be causing your chronic hives, such as allergies or an illness.
Connect with an Allergist OnlineFind an Allergist Near You

How is CSU diagnosed?

Your allergist may do blood or other tests to rule out allergies or an infection. You may also be asked to track your activities, food and drinks, exposure to common substances that can cause hives and anything that makes the hives better or worse. For the majority of people with chronic hives, no known cause is found, and a diagnosis is made by ruling out other potential causes.

Is CSU contagious?

No, CSU cannot be spread to others.

What could CSU look like?

CSU results in hives, which are raised, red bumps on the skin. These are sometimes called wheals. They can change, get bigger or join together to form larger hives, and they may disappear and reappear. Some may itch, and when they are pressed they turn white, which is called “blanching.”

For illustrative purposes only.


How long does CSU last?

CSU lasts at least six weeks and many people have it for two to five years. Some people will have it for longer than five years.

How common is CSU?

About 1.6 million people in the U.S. have CSU. That means people like you are living with CSU today. Women ages 20 to 40 are most commonly diagnosed with CSU, but can happen to anyone, of any age.

Is CSU different from hives?

Yes. Hives are a common condition that many people will experience in their lifetime. They may be caused by an allergic reaction or an illness. Most hives last a few hours or days before they go away. These are called “acute” hives, meaning they last for a brief time. Hives that last for longer than six weeks are called “chronic” hives. CSU is a different form of hives because it has no known cause. It is diagnosed by ruling out other potential causes.

How is CSU treated?

Depending on your symptoms, a doctor can help you develop an individualized treatment plan. You may benefit from speaking with an allergist, who specializes in treating hives. While there is no known cause of chronic hives, your doctor can help you manage CSU and your symptoms. To keep your hives from getting worse, your allergist may encourage you to avoid harsh soaps, use sunscreen when you plan to be outside, wear loose clothing that won’t rub against the hives and use lotions or creams that can help reduce itching.

  1. Melinda is a real patient and was compensated for her involvement in the CSU and You campaign.

Looking for additional resources?

Asthma and Allergy Foundation of America (AAFA)

Asthma and Allergy Foundation of America (AAFA), a not-for-profit organization founded in 1953, is a leading patient organization for people with asthma and allergies, and the oldest asthma and allergy patient group in the world.