Drug reactions

 NSAIDS, IV contrast, angiotensin-converting enzyme (ACE) inhibitors, etc.

Foods

Inhalation or contact with environmental allergens

Transfusion reactions

Insects

Infections-viral, bacterial, parasitic

Idiopathic-a subset with autoimmune component

Collagen vascular disease-urticarial vasculitis

Physical stimuli

 Dermatographism

 Cholinergic urticaria

 Vibration, cold, pressure, water (aquagenic)

 Sun (solar)

Mastocytosis/urticaria pigmentosa

Hereditary

 Hereditary angioedema (HAE)

 Familial cold urticaria

 C3b inhibitor deficiency

 Muckle-Wells syndrome

Schnitzler syndrome

Hypereosinophilic syndrome

Gleich syndrome