In the past, PCBs were utilized in a vast range of industrial and commercial products. These highly carcinogenic chemical compounds remain in our environment and accumulate inside organisms. Chiral PCBs are particularly dangerous because they have more chlorine atoms, which are hard for the body to break down, so they can accumulate in the body easily. Also, their isomers are metabolized differently, causing isomer-specific toxicity (particularly neurodevelopmental issues). Scientists reveal exactly how enzymes produced by the body unevenly metabolize chiral PCBs’ mirror-image isomers. These findings will improve understanding of PCBs’ toxicity in humans and other mammals.