Urticaria (also called “nettle rash” or “hives”) is common and affects 20% of people at some point in their lives. The most common form is called spontaneous urticaria. Spontaneous urticaria is divided into “acute” and “chronic” forms dependent upon whether the episode lasts less than or greater than 6 weeks.
What are urticaria (hives) and angioedema (swelling)?
Hives are characterised by itchy raised lumps (known as “weals”) on the skin that appear in a random fashion and then resolve quite quickly (by definition in less than 24 hours) without leaving a trace, although the actual condition lasts longer. The lumps can sometimes be seen visibly merging and migrating around the body or appearing as a line after scratching the skin.
Angioedema, swelling deep to the skin, may often accompany urticaria. Angioedema usually affects soft areas of skin, such as the eyelids, lips, tongue or inside of the mouth but may occur anywhere. These swellings often take a few days to clear and may be painful rather than itchy. Urticaria may present with weals alone, angioedema or both together.
What causes them?
Urticaria and angioedema are caused by the release of histamine and other chemicals from cells in the skin called mast cells. Urticaria is often thought of as an allergy but, in fact, it usually results from histamine release from mast cells due to other reasons.
Allergens in food or medicine may sometimes cause acute episodes of acute urticaria and such reactions will be characterised by the consistency of the triggers. Underlying infections can also trigger episodes of acute urticaria. However, a specific reason for urticaria is often not found particularly if it is chronic (see below).
In a small percentage of people, foods, food colouring agents and preservatives appear to worsen urticaria, and it is occasionally possible to identify these by keeping a food diary. However, as urticaria fluctuates, this is not always accurate and will not always show what is causing the problem.
If angioedema occurs without weals it may be caused by medication or an inherited illness called hereditary angioedema. This is a different problem to urticaria. It can be diagnosed with blood tests and needs different treatment.
How can they be treated?
The aim of treatment is to suppress the symptoms until the condition resolves of its own accord, rather than “curing” it.
Antihistamine tablets block the effects of histamine and should improve the itch and the rash in most people. They may not relieve urticaria completely. If urticaria occurs frequently, antihistamines should be taken regularly every day. The type, combination and dose of these drugs has to be tailored for each individual.
If antihistamine tablets are not helpful, your doctor may recommend other medicines, including montelukast, that is usually used as an add-on treatment of asthma. Immunosuppressive treatments (e.g. ciclosporin) may be beneficial for the most severely affected people, especially those with autoimmune urticaria.
Chronic urticaria (spontaneous and inducible)
What is chronic urticaria?
Chronic urticaria refers to when the urticaria and/or angioedema episodes persist for longer than 6 weeks. At any given time it is believed to affect 0.5-1% of the global population.
When a cause cannot be found, it is called ‘spontaneous’ but may have an autoimmune element to it (see below).
Another subtype of chronic urticaria are ‘inducible urticarias’ – since the weals may be set off (or “induced”) by a physical trigger, such as cold, pressure or friction. The weals usually occur within minutes, and last for less than one hour (except delayed pressure urticaria, which is delayed in onset and lasts for hours at least). They often occur in otherwise healthy young adults but can affect any age.
They include the following types:
- Symptomatic dermographism (“skin writing”) – itchy weals occur after friction, such as rubbing or stroking the skin
- Cold urticaria – itchy weals are triggered by exposure to cold, including rain, wind and cold water – swimming in cold water may be dangerous
- Cholinergic urticaria – itchy weals are triggered by sweating, following exertion, hot showers, emotional stress or eating spicy food.
- Contact urticaria – various chemicals, foods, plants, animals, and animal products, can cause weals within minutes at the site of contact.
- Delayed pressure urticaria – itchy weals develop where pressure has been applied to the skin, for example from tight clothes or from gripping tools. Usually the swelling develops several hours later. It can be painful and lasts longer than a day.
- Solar urticaria – itching and weals occur on the skin immediately after exposure to sunlight. It is rare.
- Aquagenic urticaria -small weals occur on the skin at the site of contact with water. It is extremely rare.
What causes it?
Chronic spontaneous urticaria (CSU) by definition does not have a cause but may have an autoimmune element to it, where a patient’s own antibodies are responsible for releasing histamine from mast cells. There may be a personal history or family history of other auto-immune conditions accompanying it.
What are the treatment options available?
The treatment of chronic urticarias includes the use of regular high dose antihistamines and additional medications such as montelukast. However, a significant number of patients will remain symptomatic and require additional treatments.
These might include:
- Omalizumab monthly injections. Omalizumab (a recombinant, humanized anti-IgE antibody) is an add on therapy for the treatment of CSU in adults and adolescents with an inadequate response to treatment with antihistamines.
- Immunosuppressants e.g. ciclosporin medication