Etiology
The development of asthma involves interplay between host factors (particularly genetics) and environmental exposures that occur at a crucial time in the development of immune system.
•Innate Immunity: The hygiene hypothesis suggests that certain infections early in life, exposure to other children (e.g.: presence of older siblings and early enrolment of children in childcare, which have a greater likelihood of exposure to respiratory infection), less frequent use of antibiotics, and country living are associated with a TH1 response and lower incidence of asthma, whereas the absence of these factors is associated with a persistent TH2 response and higher rates of asthma.
•Genetics: Asthma has an inheritable component, but the genetics involved remain complex.
•Environmental factors: Two major factors are the most important in the development, persistence, and possibly the severity of asthma: airborne allergens, particularly sensitization and exposure to house dust mite and Alternaria (a type of mold, common allergen grows indoors and causes hypersensitivity reactions) and viral respiratory infections.