In most cases of urticaria, there is no need for specific investigations.

• Full blood count to identify eosinophilia caused by allergy or parasitic infestation, and low white blood count from systemic lupus erythematosus.
• Thyroid antibodies and function in chronic urticaria if autoimmune origin is considered likely.
• Skin prick testing and blood tests for specific allergy (RAST, or radiollergosorbent tests, or CAP fluoroimmunoassay).
• Autologous serum skin prick test (if available) in chronic urticaria.
• Complement tests in case of angioedema without urticaria or urticarial vasculitis.
• Skin biopsy if weals are prolonged, to identify vasculitis.

Treatment of urticaria

Treatment depends on the type of urticaria, its severity and how long it has been present.

Oral antihistamines control wealing and itching for the majority of patients with urticaria. They do not affect the underlying cause of the rash. Antihistamines may need to be taken intermittently or continuously until the underlying tendency to urticaria disappears. Luckily, most people eventually recover.

Non-sedating antihistamines include:

• loratidine
• desloratidine
• fexofenadine
• levocetirizine
• cetirizine.

Cetirizine is the quickest acting of these medications, and desloratidine is the most long-lasting.

Conventional antihistamines such as chlorpheniramine or promethazine may be preferred at night as they tend to have a sedative effect. Hydroxyzine or diphenhydramine may be taken during the day and in some people they appear more effective than newer, non-sedating antihistamines.

Response and tolerance varies, so if the first antihistamine is not effective, consult your doctor. You may need to increase the dose, or use a different drug. Usually any sedative effect wears off in a week or so. Sometimes a combination of antihistamines works better than a single type alone.

Other treatments may be tried for urticaria that fails to clear with antihistamines.

• Off-license addition of H2 blockers, such as cimetidine or ranitidine, can also reduce urticaria but these medications are more often prescribed to reduce stomach acidity.
• Oral steroids (prednisone) in moderate dose for a few days are useful for severe acute urticaria. They are rarely recommended long term because of serious adverse effects. In rare cases, alternate day steroids may be warranted.
• Tricyclic medications such as amitriptyline, nortriptyline and doxepin are thought to help because of antihistaminic and neuropathic properties.
• Antileukotriene agents, such as montelukast, occasionally help; they are usually prescribed for asthma.
• Ultraviolet radiation treatment (narrowband UVB and PUVA) reduces the severity of wealing in some patients.
• Antibiotics, dapsone, sulfasalazine and antifungal agents are used to clear an assumed underlying infection or for their presumed anti-inflammatory action.
• Immunosuppressive medications. The most effective of these appears to be ciclosporin. Methotrexate, plasmapheresis and intravenous immunoglobulins) are reported to help but may have serious side effects.
• Antifibrinolytic agents (tranexamic acid, androgenetic steroids such as danazol) are mainly used for treatment-resistant angioedema or angioedema due to C1 esterase inhibitor deficiency. In emergency situations, C1 esterase inhibitor concentrate or fresh frozen plasma may be transfused.

Intramuscular injection of adrenaline (epinephrine) is reserved for life-threatening anaphylaxis or swelling of the throat.

General measures

• Do not take the medications your doctor has told you to avoid. Minimise use of aspirin and codeine. It is usually safe to take paracetamol to relieve pain. Nonsteroidal anti-inflammatories should be avoided in those that react adversely to aspirin. ACE inhibitors should be avoided in those with angioedema.
• Dietary changes may help. Some urticaria is aggravated by salicylates in certain fruits, or additives including amines, tartrazine , benzoates and other food chemicals. Whether or not these need to be avoided can be determined by appropriate food challenge tests.
• Avoid alcohol (it causes the surface blood vessels to dilate). Try not to overheat. Cool the affected area with a fan, cold flannel, ice pack or soothing moisturising lotion.