Urticaria is a common cause for referral to allergy clinics. It is characterised by the appearance of raised itchy bumps (wheals or ‘hives’) on the skin which look rather like a rash caused by nettles or mosquito bites. Understandably, an allergy is often suspected to be the cause although this is rarely the case. The symptoms can be distressing and affect sleep and/or quality of life. Minor cases may be associated with the sporadic appearance of a few occasional wheals only.
Types of urticaria
Although hives may occur during an allergic reaction, this usually resolves rapidly, i.e. within a few hours, and is also associated with other symptoms that point towards an allergic reaction having taken place.
However, urticaria rash that keep occurring – sometimes daily – is almost always not due to allergies. In this case, when the hives appear for no apparent reason, this is said to be ‘spontaneous urticaria’. This commonly goes on for weeks or months. Urticaria that stops happening in less than six weeks is called ‘acute spontaneous urticaria’ whereas hives occurring for over half of days for longer than six weeks is classified as ‘chronic spontaneous urticaria’. There are also some rarer variants in which the hives are triggered by physical stimuli such as the cold or vibration. However, acute and chronic spontaneous urticaria are the most common kinds.
Some patients with chronic spontaneous urticaria also show signs of a condition known as dermographism. In dermographism, skin redness, hives and itching can be induced by scratching the skin and it may even be possible to write words on the skin. The hives usually appear as raised lines triggered by scratching or under areas of tight clothing.
Also, some patients with urticaria can develop angioedema, which is swelling of soft tissues. Most commonly this appears as swelling of a lip or both lips, or swelling around the eye. This is often alarming for patients, but it is very rare for angioedema to be dangerous in patients who also have urticaria.
What causes hives?
Urticaria results from activation of a particular type of the immune cell – known as the ‘mast cell’ – which is resident within the skin in all people. The role of mast cells is normally to fight parasite infections. When mast cells are activated, they release granules of histamine in the skin, which cause redness, itching and swelling. In healthy individuals, mast cells are mostly dormant in the skin and not releasing these histamine granules.
There has been research conducted into why skin mast cells become activated in patients with spontaneous urticaria. In some patients with chronic symptoms, it appears that rogue antibodies sticks to the surface of these cells causing activation.
Mast cells are also responsible for allergic reactions but in this situation, they are activated by a different mechanism. An allergen – e.g. food, medication or pollen – sticks to antibodies on the surface of the mast cell and triggers activation.
Since mast cells are involved in urticaria and allergic reactions, it is quite common to confuse the two problems, but an experienced allergist should be able to tell the difference in most cases. It is also quite common to suspect ‘bed bugs’ or an ‘allergy to washing powder’ as the cause of urticaria, but these are very rarely relevant.
Brief episodes of hives (acute urticaria) lasting a few days or weeks may also occur during or following an infection or after vaccination (which mimics the effects of infection). In practice, a cause is seldom identifiable. Tests are rarely needed or useful in this situation.
Are allergy tests necessary for urticaria?
In most cases, urticaria is diagnosed by an allergy specialist based on the clinical history as there are usually features that distinguish this disorder from allergic reactions. Allergy tests should not be performed in patients who are experiencing spontaneous urticaria because the condition is not caused by allergy. The results of any allergy tests would be irrelevant to the diagnosis. Since allergy tests can occasionally give false positive results, this may also give to considerable confusion. Guidelines published by experts in the field therefore specifically advise against performing allergy tests in patients with features of spontaneous (non-allergic’) urticaria.
How to cure urticaria permanently
It is important to recognise that urticaria will eventually resolve in most patients. There is no curative treatment, but symptoms can almost always be controlled by medications in the meantime.
Popular urticaria treatments
The most important treatments for urticaria are non-drowsy antihistamines including those available over the counter such as Cetirizine or Loratadine. Where possible, sedating antihistamines such as Chlorphenamine (Piriton) should be avoided. Although the standard dose of non-sedating antihistamines is one tablet per day, many patients with urticaria require higher doses. Expert guidelines recommend up to a total of four tablets per day if necessary to control symptoms, but higher than normal doses of antihistamines should only be taken on the advice of a doctor.
If symptoms are not completely controlled, additional medications can be prescribed on top of antihistamines. If this is in turn unsuccessful, there are other effective treatments which can be used, and which are now approved by the UK Medicines and Healthcare products Regulatory Agency (MHRA). Omalizumab is an injection treatment that was originally developed to treat asthma, but which is highly effective for treatment of urticaria. However, most patients will not need Omalizumab to control their symptoms.
Dealing with hives at home
The most important treatment is to take a non-drowsy antihistamine on a regular basis and if this does not control symptoms enough, you should see your doctor to discuss increasing the dosages further. Referral to an Allergy Specialist may be needed for optimisation of treatment and to confirm the diagnosis. Urticaria in some cases can pass fairly quickly, e.g. after a few days or weeks, so it is important to be patient.
Use of steroid or antihistamine creams on the skin is unlikely to be helpful. It is also important to recognise that if urticaria is ongoing, an allergy such as to a food is extremely unlikely to be the cause and therefore dietary eliminations are not recommended. However, consumption of alcohol or use of certain anti-inflammatory painkiller medications, e.g. Ibuprofen or Aspirin may exacerbate symptoms in a minority of individuals.
Professor Stephen Till
Date reviewed: March 2022