Urticaria is characterised by weals (hives) or angioedema (swellings, in 10%) or both (in 40%).
Urticaria is classified according to its duration:
- Acute urticaria (< 6 weeks duration, and often gone within hours to days)
- Chronic urticaria (> 6 weeks duration, with daily or episodic weals)
Acute urticaria can be induced by the following factors, but the cause is not always identified.
- Acute viral infection—upper respiratory infection, viral hepatitis, infectious mononucleosis, mycoplasma
- Acute bacterial infection—dental abscess, sinusitis
- Food allergy —usually milk, egg, peanut, shellfish
- Drug allergy
- Bee or wasp stings
Chronic urticaria may be spontaneous or inducible. Both types may co-exist.
– Chronic spontaneous urticaria is mainly idiopathic (cause unknown).
Chronic spontaneous urticaria has also been associated with:
- Chronic underlying infection, such as Helicobacter pylori, bowel parasites
- Chronic autoimmune diseases, such as systemic lupus erythematosus, thyroid disease, coeliac disease, vitiligo and others
– Inducible urticaria includes:
- Symptomatic dermographism
- Cold urticaria
- Cholinergic urticaria
- Contact urticaria
- Delayed pressure urticaria
- Solar urticaria
- Heat urticaria
- Vibratory urticaria
- Aquagenic urticaria