Why are cashews never sold in their shells?

You can buy peanuts in the shell, pistachios in the shell, walnuts and almonds in the shell. But try finding a bag of cashews still in their shells at the supermarket and you will be searching for a long time. There is a good reason. Cashews come wrapped in packaging that can give you a nasty rash.

The short answer

The cashew tree belongs to the same plant family as poison ivy, poison oak and sumac, called the Anacardiaceae. The cashew shell contains an irritating oil with compounds such as anacardic acid and cardol, close chemical cousins of the urushiol that makes poison ivy itch. So cashews are always shelled and heated before they reach shops.

The real story

A cashew grows in a strange way. The seed, in its shell, hangs on the outside of a fleshy fruit called the cashew apple. Between the outer shell and the seed sits a layer of irritating oil. Shelling has to be done with great care, and it is often done by hand, sometimes by workers without proper protective gear.

The cashew apple itself is edible, but you will rarely see it outside the places where cashews grow. Its skin is so fragile that it bruises and spoils too easily to ship around the world.

The nuts are steamed or roasted at high temperatures, which breaks down the irritants, and then the shells are cracked off. That means even the cashews labelled raw in shops have already been heat-treated. Truly raw cashews in their shells are not sold to ordinary shoppers.

The system usually works well, but there have been slip-ups. In 1982 the US Centers for Disease Control reported that thousands of bags of cashews sold on the American East Coast had been contaminated with residue from the shells. About one in five people who ate them developed a rash.

The family connection runs further than you might expect. Mangoes and pistachios are relatives too. People who are sensitive to one member of the family, such as poison ivy, are more likely to react to others.

Why people get it wrong

The obvious explanation is convenience. Lots of nuts are sold shelled because cracking them is fiddly, so it seems likely cashews are just another example. It is a sensible guess, and nothing on the packet hints that there is anything more to it.

Most of us also never see a cashew in its natural state. If you had grown up near a cashew tree, the odd fruit and the oily shell would be familiar. Shoppers only ever meet the tidy, curved kernel, so the toxic wrapping is simply out of sight and out of mind.

“A nut that comes wrapped in poison ivy’s cousin. Fair play to whoever was brave enough to try the first one.”