Diagnosing urticaria 

Urticaria can usually be diagnosed by examining the distinctive red rash.

If you have long-term (chronic) urticaria, a number of tests may be needed to identify the underlying cause.

Short-term (acute) urticaria

Your GP can usually diagnose acute urticaria by examining the rash.

They'll also ask you some questions to find out what triggered your symptoms, including:

  • when and where the rash began
  • what you had to eat just before it began and details of your usual diet
  • if you started taking any new medication just before your symptoms began
  • if you live or work in an environment where you come into contact with possible triggers  such as pets, chemicals or latex gloves
  • if you were stung or bitten by an insect just before your symptoms started
  • your current state of health and if you've had any recent infections
  • if you've recently travelled to a foreign country and if so, where
  • if there's a history of urticaria in your family

In around half of all cases of acute urticaria, a cause can't be identified.

If your GP thinks your symptoms are caused by an allergic reaction, you may have to go to an allergy clinic.

Allergy testing may be needed to find out if you're allergic to suspected triggers for urticaria.

Long-term (chronic) urticaria

If your urticaria lasts for more than six weeks, it's very unlikely to be caused by an allergy, so allergy tests aren't usually recommended.

However, your GP should ask about anything that makes your urticaria worse, such as:

  • any medicines you're taking
  • your alcohol and caffeine consumption
  • your stress levels

You may also be referred for a number of tests to find out if there's an underlying cause of your chronic urticaria. These tests may include:

  • a full blood count test (FBC)  which can identify anaemia
  • tests to determine the levels of antibodies in your blood
  • a stool sample  which can identify intestinal parasites
  • an erythrocyte sedimentation rate (ESR) test  which can help to identify problems with your immune system
  • thyroid function tests  which can be used to check for an underactive thyroid gland (hypothyroidism) or an overactive thyroid gland (hyperthyroidism)
  • liver function tests  which can be used to check if you have any problems with your liver

Page last reviewed: 28/02/2016

Next review due: 31/12/2018