Breathing

Wikipedia says this about breathing.

Breathing is the process that moves air in and out of the lungs. Aerobic organisms of these types—such as reptiles, birds and mammals—require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose. Breathing is only one process that delivers oxygen to where it is needed in the body and removes carbon dioxide. Another important process involves the movement of blood by the circulatory system. Gas exchange occurs in the pulmonary alveoli by passive diffusion of gases between the alveolar gas and the blood in lung capillaries. Once these dissolved gases are in the blood, the heart powers their flow around the body (via the circulatory system). The medical term for normal relaxed breathing is eupnea.
In addition to removing carbon dioxide, breathing results in loss of water from the body. Exhaled air has a relative humidity of 100% because of water diffusing across the moist surface of breathing passages and alveoli.

Scientists are studying breathing-defects, and here are links about some of their research.

Researchers at the Columbia Center for Children's Environmental Health at the Mailman School of Public Health are the first to report an association between early childhood exposure to the chemical bisphenol A (BPA) and an elevated risk for asthma in young children. BPA is a component of some plastics and is found in food can liners and store receipts.

According to a new study from the Slone Epidemiology Center (SEC) at Boston University, African-American women who reported suffering abuse before age 11 had a greater likelihood of adult-onset asthma compared to women whose childhood and adolescence were free of abuse.