May occur together or separately. Urticaria involves only the superficial dermis and presents as circumscribed wheals with raised serpiginous borders and blanched centers; wheals may coalesce. Angioedema involves deeper layers of skin and may include subcutaneous tissue. Recurrent episodes of urticaria and/or angioedema of <6 weeks duration are considered acute, whereas attacks persisting beyond this period are chronic.
Section 12. Allergy, Clinical Immunology, and Rheumatology