ABSTRACT
Low-molecular-weight (LMW) chemicals usually induce delayed cell-mediated type IV contact allergy (i.e., allergic contact dermatitis). Contact urticaria, in turn, is usually caused by proteins, which are large molecules. Some LMW chemicals, however, may induce immediate-type contact reactions (contact urticaria). These chemicals often also cause respiratory symptoms, asthma and rhinitis, and anaphylactic multiorgan symptoms. Concomitant contact urticaria and respiratory diseases are common in occupational settings. Some chemicals induce immunoglobulin E (IgE)-mediated type I allergy, but in most cases the mechanisms are unknown.
