Elliott et al. function (ATSDR 2004). Although reductions in pulmonary function can be transient and do not necessarily reﬂect permanent adverse health effects (ATS 2000), they generally precede per- manent effects. Thus, chronic reduction in FEV1 is a sentinel event for adverse health effects from inhaled exposures, such as air pol- lution (ATS 2000). In particular, FEV1 has been identiﬁed as a risk factor in cardiovascular disease, stroke, and lung cancer, as well as an important predictor of all-cause mortality (Hole et al. 1996). It is probable that most exposures to 1,4-DCB are chronic, rather than acute and sporadic, because 1,4-DCB is a component of household products used for prolonged peri- ods. For example, air fresheners, toilet bowl deodorants, and mothballs are used until their emissions cease, and then they are replaced. Staff interviewers in the SHIELD study, where blood concentrations of 1,4-DCB were high, noted that many children’s homes had pervasive scents of air fresheners (Sexton et al. 2005a). In NHANES III, 32.1% of the par- ticipants in the VOC study reported recent use of air fresheners or room deodorizers. Fewer participants reported recent use of toi- let bowl deodorants (8.7%), although their use was associated with a 2-fold increase in odds of having high 1,4-DCB blood levels (Churchill et al. 2001). Because NHANES III is a cross-sectional study, measurements of exposure and out- come were made at the same time, and it is not possible to determine if 1,4-DCB expo- sure preceded pulmonary function decline. A longitudinal study measuring pulmonary function and exposure to 1,4-DCB at various time points would be necessary to evaluate the temporality of this relationship. Although it is possible that people who are exposed to toilet bowl or air fresheners and other room deodorizers might also be exposed to cleaning products that impair pulmonary function, we had no data to address this. The inverse association between 1,4-DCB concentration and pulmonary function may have been affected by unmeasured con- founders. We assessed the inﬂuence of other factors that may be related to pulmonary function and to 1,4-DCB exposure, such as type of heating, use of wood fires, age of house, presence of furred pets, occupation, socioeconomic status, presence of environ- mental tobacco smoke, smoking history, and diagnosis of asthma or emphysema. Only emphysema confounded the relationship between 1,4-DCB and pulmonary function deficits. The ability to carefully adjust for smoking with several variables, including the objective measure of environmental tobacco smoke exposure, serum cotinine, was a con- siderable strength of our analyses. 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