Lung damage may take place after a single exposure to an irritant gas, fume, or vapor. It is surprising that, although thousands of persons experience accidental high-level irritant exposure each year and seek medical care, a majority recover and few persons die. Some of the affected manifest residual impairment, which may take longer to resolve; in these cases host factors such as cigarette smoking or preexisting lung diseases come into play. If the intensity or toxicity of the exposure is great, consequential outcomes may be upper airways damage (corneal damage, swelling of the tongue, persistent rhinitis, closure of the glottis and larynx), asthma, adult respiratory distress syndrome, or persistent bronchiolar obstruction (bronchiolitis obliterans). For repeated moderate-level irritant exposure, there may initiation or exacerbation of asthma, fall in ventilatory function, increased airway responsiveness, enhancement of the cough reflex or changes in exhaled breath and induced sputum parameters. A number of conditions can mimic irritant-induced asthma and differentiation is important. Such entities include vocal cord dysfunction and sensory hyper-reactivity. Although bronchiolitis obliterans usually follows inhalation of a gas such as nitrogen dioxide, a new type of bronchiolitis obliterans is reported for popcorn workers exposed to high levels of diacetyl, an agent used in the popcorn flavoring. It is important to control irritant exposures because they can be consequential for many workers.