Causes and assessment of urticaria

Urticaria (also known as hives or wheals) is characterised by transient erythematous lesions that vary in size and are often oedematous. Deeper subcutaneous swelling (angioedema) may coexist. Superficial swellings tend to be itchy, while deeper swellings can be painful. The cause of urticaria can rarely be established based on appearance.

Urticarial lesions persist for a few minutes to 24 hours. Episodes of urticaria involve individual urticarial lesions ‘coming and going’.

Consider anaphylaxis if urticaria is associated with respiratory, gastrointestinal or cardiovascular symptoms.

If individual lesions persist for more than 24 hours, and are not itchy, consider urticarial vasculitis, erythema multiforme and erythema nodosum.

Acute urticaria is most commonly caused by infection (most commonly viral upper respiratory tract infection), drug allergy (eg antibiotics, nonsteroidal anti-inflammatory drugs [NSAIDs]) or immunoglobulin E (IgE)–mediated food reaction. Contact with certain substances (eg latex rubber gloves, some foods, animal saliva) occasionally causes urticaria (contact urticaria), and removing this contact leads to resolution. Physical factors (eg rubbing or stroking skin, cold, pressure) can exacerbate acute urticaria.

Specific investigations are rarely required for acute urticaria. However, if there is history of exposure to a likely triggering agent (eg food, drug) in the 1 to 2 hours before onset of urticaria, and the urticaria has lasted for up to 24 to 48 hours, consider referral to a clinician with expertise in allergy for allergy testing (eg serum specific IgE, skin testing). There is limited use for allergy testing in acute urticaria lasting for more than 24 to 48 hours because it is unlikely that an allergy (eg to food or drug) is the cause.

In the majority of chronic urticaria cases (episodes of urticaria persisting for more than 6 weeks), a specific triggering agent will not be found. However, it can be associated with chronic infection, connective tissue disease, an autoimmune condition (especially autoimmune thyroid disease), or autoreactivity (immunoglobulin G [IgG] antibodies to a component of the IgE receptor).

Obtain a thorough history and perform a physical examination, particularly aiming to identify any underlying infection or associated systemic autoimmune condition. Patients typically report certain physical triggers such as heat, cold, pressure, or rubbing or scratching of the skin (dermographism). Some patients report an increase in symptoms with stress, sleep deprivation, or at certain times during their menstrual cycle. Laboratory testing (other than those to exclude potential associations) and allergy testing are rarely useful for chronic urticaria (because it is unlikely that an allergy is the cause).

Patients with chronic urticaria may benefit from minimising the use of drugs that can aggravate the condition (eg aspirin, NSAIDs, opioids). Evidence for the benefit of elimination diets is poor.

Physical urticarias are urticarias caused solely by a physical stimulus. The mechanism is not clear, but histamine has a role in most types—see Physical urticarias for more information. Physical urticarias are treated as for acute or chronic urticaria.