The cause of<unk>  is not fully understood; however, several mechanisms have been proposed. Interaction between water and a component in or on the skin or sebum has been suggested. This theory suggests that a substance is formed by this interaction, the absorption of which causes perifollicular mast cell degranulation with release of histamine.
Aquagenic urticaria
Cold urticaria
Solar urticaria
Cholinergic urticaria
Heat urticaria
Pressure urticaria
Delayed pressure urticaria
Adrenergic urticaria