Isocyanates are direct irritants to the respiratory tract. Their toxicity can result in fatality. Atopy does not play a predisposing role. Immunological mechanisms involving the anti-bodies IgE and IgG have been demonstrated. Other mechanisms involving bronchial beta-receptors or the inhibition of cholinesterase have also been suggested.
Bronchial response can be either immediate or delayed.
Sensitized subjects may be intolerant to cruciferae. Cases of fatal asthma have been recorded. Diferences in sensitization to monomers and prepolymers may occur. The norms for tolerable levels of these monomers are not sufficient to prevent work-related asthma. No norms have been fixed for polyisocyanates or prepolymers.