Researchers discovered that a common agricultural fungicide can cause fungal cells to change their genetic structure in ways that make them resistant to medicines used to treat human infections. The fungus Candida tropicalis can switch to a haploid state (single copy of genes instead of two) when exposed to this agricultural chemical, and these altered cells become resistant to both agricultural and medical antifungal drugs. This explains how resistance that develops in agricultural settings can spread to clinical settings, creating a public health threat.