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Chronic Spontaneous Urticaria (CSU) Frequently Asked Questions (FAQ)

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Q 1: What is CSU?

Chronic spontaneous urticaria (CSU) is the medical term for hives (the common term for urticaria) that are chronic (lasting six weeks or more, three to four times per week), and spontaneous (with no known trigger).

Symptoms of CSU can be similar to other types of hives, which:

  • Are red, white or skin coloured itchy blotches or lumps, that can be mistaken for mosquito bites.
  • Vary in size (from a pin head to a dinner plate) and can occur on any part of the body.
  • Usually last for less than 24 hours, and then show up later in another location on the body.

Some people who have CSU will also have angioedema, which are sudden swellings of different parts of the body, such as lips, eyelids, hands or feet, that can last up to several days.

Q 2: What causes hives?

Hives occur when histamine-containing mast cells, which are found under the lining of the skin, are activated and release histamine (and other chemicals) into the tissues. Histamine irritates nerve endings to cause itching, and makes blood vessels expand and leak, which causes redness and swelling.

Up to one in five people have hives at some time during their life. Common causes of hives include infections and contact allergy to plants or animals. Although hives can be part of an allergic reaction, hives that last for more than a few days are usually not caused by allergy. CSU can sometimes be caused by an underlying medical condition, but in most cases the cause of CSU is unknown (spontaneous or idiopathic).

Q 3: How is CSU diagnosed?

CSU is diagnosed when a person has spontaneous hives for more than six weeks, without any allergic cause. To confirm this diagnosis, your doctor will:

  • Review your medical history (It can be helpful to keep a diary and a photo record of the hives), followed by a detailed physical examination.
  • Order blood tests if an underlying condition is suspected. Allergy tests are usually not required unless there is a reason to suspect an allergic cause.

People with severe CSU symptoms that affect their daily life, and do not respond to simple treatment should be referred to a clinical immunology/allergy specialist for assessment and consideration of additional treatments.

Q 4: How is CSU treated?

Whilst most cases CSU resolve within a few weeks without any specific treatment, sometimes CSU can last for months or longer. The goal of treatment is to reduce or suppress itch and hives, whilst minimising side effects.

Non-drowsy antihistamines are often used to relieve itch, and higher than standard doses may be required. Severe CSU that is not controlled with high dose antihistamines can require specialised treatment, including:

  • Immune modulators - Usually given as subcutaneous injections into the tissue between the skin and the muscle that can be given at home.
  • Immunosuppressive medications - Corticosteroids can be used to treat severe symptoms for a short time.

Options for long term treatment should be discussed with your specialist.

© ASCIA 2022

Content updated February 2022

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ASCIA is the peak professional body of clinical immunology/allergy specialists in Australia and New Zealand