Etiology of Reactive Airway Disease

Genetic and Host Factors

Reactive airway disease is fundamentally a chronic inflammatory disorder caused by the complex interplay between genetic susceptibility and environmental exposures, particularly allergen sensitization, respiratory infections, occupational exposures, and irritants 1
Parental history is the strongest predictor: 80% of children with two asthmatic parents develop the disease compared with 40% with one asthmatic parent and only 10% with no asthmatic parents 2
Sex influences disease development: males develop disease 2-4 times more frequently than females in the first 3 years of life, though females are more likely to have persistent disease after puberty 2

IgE-mediated inhalant allergen exposures induce both airway inflammation with eosinophils and airway hyperresponsiveness, with indoor allergens including house-dust mites, animal proteins, cockroaches, and fungi 1, 4
Outdoor allergens, such as pollen and outdoor molds, also contribute to the development of asthma 4
Viral respiratory infections are the most common cause of asthma symptoms in children 5 years and younger 3
Workplace exposures are responsible for 15-25% of asthma in adults, with high-molecular-weight agents and low-molecular-weight agents acting as common causes 2
Environmental tobacco smoke exposure facilitates asthma development in children, with increased risk and severity in children of parents who smoke 4
Personal smoking interacts with airway responsiveness and is associated with higher likelihood of new-onset or recrudescent asthma in adulthood 2

The underlying inflammation involves multiple cell types, including mast cells, eosinophils, neutrophils, T lymphocytes, macrophages, and epithelial cells 1
Inflammatory mediators, including histamine, tryptase, and leukotrienes, are released during exercise or exposure challenges 5

Exercise-induced bronchoconstriction occurs through specific environmental mechanisms, including cold, dry air inhalation, trichloramines in indoor pool air, and high allergen and ozone environments 5