Nettle rash

Acute urticaria

Acute urticaria is usually diagnosed by examining the rash on your skin. Your GP will also want to find out what triggered the urticaria, so you can avoid it in future.

They will ask you:

• when and where the episode began
• what you had eaten just before the urticaria started and what you normally eat
• whether you had started any new medication just before the symptoms began
• whether you live or work in an environment where you come into contact with any possible triggers, such as pets, chemicals or latex gloves
• if you had any insect stings or bites just before symptoms started,
• about your current state of health, particularly if you have had any recent infections
• if you have recently travelled to a foreign country and, if so, where
• if there is a history of this condition in your family

A cause is never identified in half of cases.

If your GP strongly suspects a link to an allergic substance, you may be referred to an allergy clinic. Tests may be performed on either your skin or your blood to see if you are allergic to suspected triggers for urticaria, particularly foods and latex.

Chronic urticaria

If your urticaria persists for more than six weeks, it is extremely unlikely that it is due to an allergy, so allergy tests are normally not recommended.

However, your GP should ask about any factors that can make your urticaria worse, such as medicines, your alcohol and caffeine consumption, and stress levels.

You may also be referred for the following tests to see if there is any underlying cause of your chronic urticaria:

• a full blood count test, which can identify anaemia
• 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 check whether you have an over- or underactive thyroid gland
• liver function tests, which can check whether you have any problems with your liver.