Figure 8: Factors involved in induction and exacerbation of asthma.
Induction of asthma may occur in genetically susceptible people
upon exposure to common allergens or certain chemicals. Nonspecific
irritants and promoters may facilitate induction through injury and
increased uptake of allergens or by modulating immune responses (dashed
arrow). Both allergens and irritants may exacerbate existing asthma.