IGHE and Airway obstruction: Assuming that genetic susceptibility is randomly distributed across occupational groups, the unequal distribution of occupational asthma cases is related primarily to (i) the presence or absence of a latency period of airway obstruction associated mostly with allergic (IgE mediated) or irritant-induced asthma, respectively, (ii) the agent to which workers are exposed (low- vs. high-molecular-weight > 5 kDa), (iii) the duration of exposure and the agent concentration [57,58].