Phenotypic differences and similarities in the spectrum of occupational asthma (OA) subtypes reflect the underlying mechanisms of the diverse forms of the disease, and these phenotypes provide information as to diagnostic steps and approaches to management. In large part the phenotype reflects the existence of immunologic mechanisms and presence or absence of a specific IgE-antibody response to a work sensitizer. However, further differences occur between OA from high and low-molecular weight sensitizers (chemical sensitizers), that potentially might be relevant for non-occupational asthma. Chemical sensitizers cause a specific response which is more likely to be a late asthmatic response and specific IgE can only be identified in a minority. Irritant-induced asthma is most easily recognized when it occurs with one or more high level respiratory irritant exposure(s) but is also possible with chronic low-level exposures as in cleaners, farmers and woodworkers, as suggested from epidemiologic studies. Occupational asthma COPD overlap is more common in older patients and with OA from low-molecular weight sensitizers. Removal from exposure to the causative agent is currently advised for those with OA from sensitization: further studies with omalizumab and other biologic agents are needed to determine whether these might allow return to the same exposure.Copyright © 2020. Published by Elsevier Inc.