There is an increase in the incidence of asthma and rhinitis from children to subjects of 30 years old in recent years. Allergy reaction is initiated by the presentation of an allergen to T cells and the chemical mediators released from mast cells by the interaction of an allergen specific IgE and the IgE receptor(Fc RI). Interleukins from Th2 type T cells and the mast cells cause chronic allergic inflammation. We review here the signal transduction in mast cells and the allergic capacity of environmental factors. Signaling starting from the receptor has been clarified as a cascade of two types of phosphorylations in mast cell and lymphocyte. Characterizations of interleukins and allergens have also been done remarkably. Environmental modifications are implicated as the recent increase of allergies in various ways: new lifestyle habits, changes in clothing, housing, diet and atmospheric pollution. Multiple factors are recognized for their increase of the amount of some antigens such as molds, house dust mites, pollen, peanut, latex or for the adjuvant or signal-modulating effects such as fossil fuel combustions, various polluting gas and lipids. Pollinosis by Japanese Cedar is potentiated by both increased pollen and diesel exhaust particles. And vanadium and formaldehyde activate mast cells directly to release chemical mediators.