Atopy is the inherited predisposition to develop an antibody called immunoglobulin E (IgE) in response to exposure to environmental allergens.  This can be measured in the blood.

Additionally, the “hygiene hypothesis” is also noted as a reason for the development of asthma.  The hygiene hypothesis states that emphasis on hygiene and sanitation of the “Western lifestyle” has lead to a decrease in childhood infections.  Children are no longer experiencing the same exposures and infections as they used to leading to an increase in risk for asthma.