Table 1.

Known and presumptive factors though to influence the development and persistence of asthma during early childhood.

Known or suspected determining factors	Strength/direction
Wheezing viral infection	+++
Febrile viral infection	+++
Sensitization to perennial aeroallergens	+++
Sensitization to other classes of allergens	++
Age of infection and type of virus	++
Genetic predisposition to Th2 immune bias	++
Daycare	+
Sex	+
Maternal smoking	+
Postnatal tobacco smoke exposure	+
Maternal and antenatal infection (and antibiotic use)	+
Bronchial hyperresponsiveness	+
Low-lung function/lung growth	+
Mucosal inflammation	+
Obesity	+
Lung microbiota	+
Cesarean delivery	+
Maternal and antenatal environmental exposure	++/−−
Domestic animal exposure	+/−
Microbiota development in gut	+/−
Maternal and antenatal nutrition	+/−
Number of siblings	−

Once identified, such factors can be measured and the data introduced into modeling systems to generate and test hypotheses on asthma development.

“+” contributes to etiology/pathogenesis and “−” protective.