Although the etiology of urticaria is mostly unclear, there are a number of recent new insights into the underlying pathomechanisms and causes. Dermal mast cell numbers and endothelial cell adhesion molecule and cytokine expression are also increased in uninvolved skin, while serum P-selectin levels are elevated, suggesting a systemic activation of the cutaneous inflammatory system in urticaria. In all adults, but not children with indolent mastocytosis, we found activating point mutations of c-kit, the mast cell growth factor receptor, in lesional cutaneous mast cells. In acute urticaria, IgE-dependent mechanisms are only rarely involved (0.9%), in contrast to generally held beliefs, whereas acute upper respiratory infections (39.3%) and drug intolerance (9.2%) are more frequent. In chronic urticaria, pseudoallergies to food (73%) and more rarely chronic inflammatory gastrointestinal diseases (11%) play a major role, with avoidance or elimination of the eliciting factors leading to long term remission. On the basis of recent findings, autoantibodies must be viewed mostly as secondary rather than causative in chronic urticaria.