Objective: Consistent evidence has shown seasonal peaks in suicide incidents but the explanation remains elusive.We proposed that seasonal aeroallergens represent environmental triggers for suicide through the association between depression and allergy as well as the depressogenic and prosuicidal effects of certain cytokines, and therefore examined the associations between pollen exposure and suicide, between allergy and suicide with data from a large population.Methods: Using data from Danish population longitudinal registers, we retrieved all defined suicide deaths over a 26-year period in Denmark, recorded daily data of air pollen counts, and personal information on diagnosed allergy, psychiatric illness and socioeconomic status.We assessed suicide risk in relation to pollen concentration and allergy history with conditional logistic regression.Results: We found that a spring peak of suicide was present in all suicides, and was significantly more prominent in those with a history of mood disorders, independent of gender, suicide method and personal socioeconomic status.We have also noted that significantly more suicide victims, compared with sex-age-matched population controls, had a history of allergy treated in hospitals, and that the overall allergy predicted suicide completion with odds ratio of 1.35 in men and 2.02 in women and such association remained after controlling for personal socioeconomic status and history of mood disorders.When modelling the frequencies of suicide deaths with the seasonal data of pollen counts suicide frequencies, we have observed a significant dose-response correlation between pollen counts and suicide incidents.Conclusion: These findings support a biological connection between allergy, mood disorder and suicidality for which pollen may act as a triggering factor.However, additional studies are necessary to confirm this novel hypothesis which carries a promising potential for suicide prediction and prevention.