High Pesticide Exposure Events and Self-Reported and Measured Olfactory Dysfunction

Importance Pesticide exposure may contribute to olfactory dysfunction in adults, but empirical evidence is limited. Objectives To examine the association between high pesticide exposure events and olfactory dysfunction in farmers. Design, Setting, and Participants This survey study used data from a subcohort of the Agricultural Health Study (AHS), the Pesticide and Sense of Smell (PASS) Study, conducted from January 2020 to October 2021. Participants included farmers from Iowa and North Carolina, were alive as of June 2019, and either reported olfactory dysfunction in the AHS phase 4 survey or were randomly sampled from those reporting normal olfaction. Statistical analysis was conducted from August 2023 to December 2025. Exposure High pesticide exposure events self-reported in the PASS Study and the AHS phase 1 through 3 surveys. Main Outcomes and Measures The main outcome was olfactory dysfunction first self-reported and then measured using the 12-item Brief Smell Identification Test (defined as a score ≤8). To extrapolate PASS Study findings to the target population, inverse probability weights were constructed to account for death and study nonparticipation. Results This analysis included 2545 of 4629 farmers (55.0%) who completed the study activities, including a survey and a smell identification test (mean [SD] age, 70.3 [9.6] years; 2467 [96.9%] male). The weighted prevalence of self-reported olfactory dysfunction was 21.2% (95% CI, 18.1%-24.3%) among farmers with a history of HPEEs and 15.1% (95% CI, 12.9%-17.3%) among those without, corresponding to a relative risk (RR) of 1.30 (95% CI, 1.04-1.62). The exposure was not associated with olfactory dysfunction identified from the smell test (RR, 0.97; 95% CI, 0.83-1.15) or with the farmers’ perceived testing experience, including reporting substantial difficulty in identifying odorants (RR, 0.94; 95% CI, 0.78-1.13) and reporting the odorants as weak (RR, 1.01; 95% CI, 0.78-1.30). Results were similar when using exposure data from previous AHS surveys. Conclusions and Relevance This survey study found that HPEEs were associated with subjective reports of olfactory loss among farmers but not with their measured smell identification. These findings underscore the importance of incorporating both objective and subjective measures of olfaction in epidemiologic research.