What is Urticaria (Hives)
Urticaria, which is also known as ‘hives’, ‘weals’ or ‘nettle rash’, is a red, raised and itchy rash caused by swelling of the upper layers of skin. Depending on the timescale of symptoms, urticaria may be classified into two types: acute and chronic. In acute urticaria, the rash completely disappears within six weeks (most cases resolve within 24 – 48 hours). By contrast, the symptoms of chronic urticaria either persist or come and go over a period greater than six weeks. Acute urticaria is a very common condition, affecting 1 in 6 people during their lifetime. Chronic urticaria is less common, affecting about 1 in every 1000 people.
There are a number of causes which range from allergic reactions to unknown causes (see causes). Treatments for Urticaria or hives depend on the severity of the condition and range from home treatments with creams or anti-histamines to stop the itching to prescription medications (see treatments).
The main symptom of urticaria is an itchy, red rash. Characteristically, the rash has well-defined, raised swellings known as ‘wheals.’
Wheals are typically red or white and vary in shape – some are circular or ring shaped, others may look like areas on a map (geographic wheals). They also range in size from a few millimetres across to several centimetres. Occasionally, wheals may join together to form larger ones. Applying pressure to a red wheal causes it become white. This is termed ‘blanching.’
Wheals are generally surrounded by areas of red (erythematous) skin known as ‘flares’. Flares may persist for slightly longer than wheels. Together, wheals and flares have an appearance similar to the rash caused by stinging nettles.
In some cases, urticaria may cause swelling of the lips, tongue eyelids, genitals, hands, feet. This is known as angioedema. Urticaria and angioedema may also be signs of anaphylaxis – which is a severe allergic reaction e.g. to peanuts or insect stings. Anaphylaxis can cause breathing difficulties and shock and is a medical emergency.
Urticaria is thought to be caused by the release of inflammatory substances in the skin, one of which is called histamine. These substances cause blood vessels in the skin to become more leaky, allowing fluid to leak out and form swellings / wheals. The inflammatory substances also cause blood vessels to dilate, which gives rise to red ‘flares.’
The cause of the inflammatory reaction is not known in 50% of cases of acute urticaria. Clinicians term this “idiopathic urticaria.” In the remainder of cases, there are often identifiable triggers that cause the rash. These include allergies, viral infections, nettle stings and skin contact with certain substances. Physically rubbing the skin may also trigger urticaria – this is known as ‘physical urticaria.’
Chronic urticaria is thought to be caused partly by an autoimmune reaction, whereby the body’s immune system attacks itself. Chronic urticaria is also sometimes associated with other autoimmune conditions such as rheumatoid arthritis, systemic lupus erythematosus and some thyroid diseases.
There is also a link between chronic urticaria and parasitic infections, viral hepatitis and certain cancers.
A GP may diagnose urticaria based on the appearance of the rash. The doctor may ask you further questions regarding how long you have experienced symptoms, whether there are any known triggering factors, and whether you have any other illnesses.
Further tests are sometimes required to identify the underlying cause of urticaria, particularly chronic urticaria. These may include:
- Full blood count – this blood test looks at the amount of red blood cells, white blood cells and platelets and can help rule out signs of anaemia or infection.
- Thyroid function tests – this blood test looks at the function of your thyroid gland and can rule out hypo- and hyper-thyroidism.
- Erythrocyte Sedimentation Rate – this is a blood test which can help rule out inflammation or problems with your immune system.
- Stool sample – this can be used to rule the possibility of intestinal parasites
- Liver function tests – this blood test looks for signs of liver damage.
Referral to a specialist
In the event your GP suspects an allergy is causing your urticaria, you may be referred to an allergy clinic for further testing.
You may also be referred to a dermatologist or immunologist if your urticaria is not well controlled on current medication.
Mild cases of acute urticaria generally go away on their own (over 24 to 48hours) and do not require treatment. Urticaria that is more persistent may be treated with antihistamines. More severe symptoms of urticaria may require steroid medication.
Antihistamines block the effect of histamine, the inflammatory substance released in urticaria, and help treat itchiness and redness. Antihistamine drugs include: cetirizine, fexofenadine and loratidine and are generally taken daily for up to six weeks. These are known as non-sedating antihistamines as they do not cause drowsiness. A sedating antihistamine (such as chlorphenamine) may be more suitable for itchiness that keeps you awake at night.
Menthol cream and camomile lotion
Menthol cream helps to reduce itchiness and is applied directly to the skin. It may be used instead of or in addition to antihistamines. Camomile lotion can also ease itchiness and is available from most pharmacies.
Severe symptoms in chronic urticaria can be treated with a short course of oral corticosteroids. Corticosteroids are drugs such as prednisolone, which act to dampen down the immune system and reduce inflammation. They are taken for a period of 3-5 days, usually in combination with an antihistamine.
Long-term use of corticosteroids is discouraged as it can cause side effects such as high blood pressure, thin skin and cataracts.
A specialist may consider prescribing ciclosporin in very severe cases of chronic urticaria. Ciclosporin works by suppressing the immune system and preventing autoimmune damage.
The drug has potentially serious side effects such as kidney damage and increased vulnerability to infection. As a result, you will need to have blood tests to monitor your health when taking ciclosporin.
Omalizuab is a newer treatment and is a type of “biologic” drug. It works by blocking the effects of an antibody (IgE) that is responsible for inflammatory reactions in chronic urticaria. Omalizuab is given as an injection and is generally only available from specialist clinics. Side effects of omalizuab include nausea, headaches and joint pain.
Avoiding triggers of urticaria can help to reduce the frequency of symptoms. This may involve modifying your diet to avoid certain foods, telling your GP about any medications that trigger urticaria and altering your work or home environment to avoid direct contact with triggering chemicals.
Acute Urticaria. Patient.info. Available online at: http://patient.info/health/acute-urticaria-hives
Chronic Urticaria. Patient.info. Available online at: http://patient.info/health/chronic-urticaria-hives
NICE CKS. Urticaria. (May 2016). Available online at: https://cks.nice.org.uk/urticaria
Urticaria. Patient.info – Professional Reference. Available online at: http://patient.info/doctor/urticaria-pro
Urticaria (hives). NHS Choices. Available online at: http://www.nhs.uk/Conditions/Nettle-rash/