Urticaria classification

There are numerous types of urticaria. Based on the way wheals appear, they can be divided into spontaneous and physical urticaria. Spontaneous urticaria is further divided into acute and chronic urticaria, based on their duration. Mechanical forces and pressure on the skin or the ambient air temperature are responsible factors in development of physical urticaria, which can be divided into more subtypes, such as demographic urticaria, delayed pressure urticaria, cold contact urticaria, heat contact urticaria, solar urticaria and vibratory urticaria. Besides these two main classes of urticaria there are other particular types such as, cholinergic urticaria, adrenergic urticaria, aquagenic urticaria, contact urticaria and drug-induced urticaria.

Urticaria may be classified according to roles of triggers into two subtypes:

• • Acute urticaria: Spontaneous appearance of wheals, most days in a period less than 6 weeks.
  • Chronic urticaria: Spontaneous appearance of wheals with more than 6 weeks duration.^[3]
    • Chronic continuous: Involvement in every day or most days.
    • Chronic recurrent: There are symptom free intervals.

• • Dermographic urticaria (factitial urticaria): Appearance of wheals 1-5 minutes after a mechanical shearing force, which mainly involves young adults.
  • Delayed pressure urticaria:
    • Appearance of wheals 3-8 hours after a vertical pressure, which usually lasts for 8–48 hours.
    • Frequently seen on palms and soles, buttocks and back (sitting on a hard chair).
  • Cold contact urticaria:^[6]
    • Appearance of wheals due to cold temperatures, such as ice and cold air, water, or wind.
    • It is divided into primary and secondary subtypes. In primary form there is no known trigger causing the urticaria, besides cold temperature. Nevertheless, secondary form of cold contact urticaria is also associated to other triggers in addition to cold temperature, such as medications, bacterial or viral infections, hymenoptera stings, immunotherapy and hematological malignancies.
  • Heat contact urticaria
  • Solar urticaria: Appearance of wheals due to sunlight/ultraviolet light with wavelengths ranging between 280 and 760 nm.
  • Vibratory urticaria: Appearance of wheals due to vibratory forces, such as pneumatic hammer.^[7]
  • Cholinergic urticaria:
    • Usually due to causes that elevate core body temperatures, such as exercise, emotional stress and passive warmth (hot shower) and less commonly due to alcoholic drinks or warm or spicy foods.
  • Adrenergic urticaria:
    • Elicited by stress
  • Aquagenic urticaria
    • Urticaria appearance is not due to water itself, nevertheless water delivers some water-soluble allergens to the dermis.
  • Contact urticaria (allergic or pseudoallergic)
    • Chemical substances contact (such as industrial chemicals, animal product, textiles, plants, drugs, cosmetics and food) with skin leads to urticaria appearance.
  • Drug-induced urticaria (such as aspirin-intolerant chronic urticaria (AICU))

‡ Can also be classified as physical urticaria.

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