Why does cilantro taste like soap to some people?

Cilantro tastes like soap to some people partly because of their genes, and above all because of how their nose reads a family of molecules called aldehydes. Coriander's aroma comes from about half a dozen substances, most of them aldehydes, and some of those same aldehydes turn up in soaps and detergents. A gene called OR6A2 builds a smell receptor that is highly sensitive to aldehydes. People with certain variants of it are especially sensitive to the offending ones, and may even miss the pleasant aromas everyone else enjoys. Where most people taste something fresh and lime-like, they get soap, or worse.

The evidence for a genetic role is neat. About 80% of identical twins share the same opinion on coriander, while fraternal twins agree only about half the time. A genetic survey of nearly 30,000 people then found two variants linked to how coriander is perceived, the more common one in a gene involved in smelling.

Genes aren't the whole story, though. Dislike ranges from 21% of East Asians to just 3% of Middle Eastern people, and it is lowest where coriander is common in the cuisine. Those numbers say nothing about how common the gene variant is: they describe tastes, not genes.