Clinical evidences and epidemiological studies show that allergic pathologies of the respiratory tract are increasing in the world areas with high pollution impact, demonstrating how many polluting substances favor both allergic sensitization and the bronchial inflammatory changes characteristic of asthma. It has been shown that asthma, as many other diseases, is a complex interaction between genetic predisposition and environmental stimuli that results in clinical expression of various phenotypes of asthma: allergic, intrinsic etc. Many pollutants have such a potential. Diesel exhaust particles (DEP) can favor allergic sensitization, induce acute asthma attacks and increase bronchial reactivity, acting both on allergen, on bronchial mucosa and on immune cells. In fact, DEP can favor B lymphocytes to shift to a production of IgE and T cells to produce Th2 cytokines. Asthma can be also induced by high exposure to many other substances as NO2 and first of all ozone (O3): strong oxidizing substance that is synthesized, in absence of ventilation, by photochemical reaction due to the combination of ultraviolet sun radiation on exhaust gases as NO2 and hydrocarbons. Ozone is abundant in cities with minimal concentration in the morning gradually increasing during the day until maximal levels in the afternoon and then decreasing during the night. Epidemiological studies show that the number of access to hospital for acute asthma and even the use of bronchodilator by asthmatics increase during the high level periods when Ozone constitute almost 90 percent of the total oxidants in the environment. Particulate matter of very small diameter have a crucial role in favoring asthma attacks, and smaller the substance deeper the penetration in the bronchial tree, with an inflammatory reaction in the peripheral bronchial mucosa characterized by increased vessel permeability, mucosal edema, inflammatory mediator production by damaged epithelium and inflammatory cells that determines acutely a high narrowing of the bronchial lumen and in a long period favor airways remodeling and a rapid decline of respiratory function.