A mixed effects model will be used to estimate all effects and pertinent contrasts will be used to test the hypotheses. Specifically, models will include exposure (CA or DBP), order (CA before DBP or DBP before CA) and gene variant status (e.g., GSTM1 present or GSTM1 null) as fixed effects and subject identifying number as a random effect. The inhalation allergen challenge is given during both DBP and CA exposures and will therefore not be included in the statistical analyses.