Cashews are a popular tree nut consumed around the world. They’re considered to be nutritious and may offer numerous health benefits, such as improving blood sugar control among people with type 2 diabetes and reducing total and LDL (bad) cholesterol.
Some people enjoy eating cashews on their own, blended into cashew nut butter, or puréed into a dairy-free cream for soups, sauces, and ice cream. However, many people are unaware that eating cashews in certain forms can be harmful, as they contain a dangerous toxin called urushiol.
This article examines what makes certain cashews poisonous and how to enjoy these tree nuts without risk of toxicity.
Cashew harvesting and processing
Cashews grow on cashew trees (Anacardium occidentale). As such, they’re classified as a type of tree nut. Mature cashew trees grow red or yellow pear-shaped drupes called cashew apples. The cashews themselves grow inside of gray shells on the ends of those fruits.
The cashews are ready for harvesting when the cashew apples begin to fall from the tree. The cashew apples, which are edible but highly perishable, are collected.
The cashew nuts, still in their shell, are removed from the ends of the fruits and may be dried in the sun, depending on the manufacturer’s process. These cashews are raw and not sold due to a risk of urushiol exposure.
The raw cashews are then roasted at high heat, either by steaming them in a large rotating drum or vat of boiling oil to remove urushiol remnants before they can be shelled, thoroughly dried, and peeled.
At this point, these cashews are still often labeled as raw, since they’re free of added flavorings.
Cashews may be roasted a second time for flavoring purposes if they’re being sold as roasted cashews. Another round of roasting may also help ensure any remaining urushiol residue is removed before sale.
Commercial cashews are then ready for quality checks, packaging, and sale.
Truly raw cashews are still in their shell, which cannot be eaten. Even cashews sold as raw have been roasted once after being carefully harvested and shelled to remove any toxic oil residue.
What toxins do they contain?
Cashews naturally contain a toxin called urushiol. Urushiol is a substance found in all members of the Anacardiaceae family of trees, which includes cashews, mango, poison ivy, poison oak, sumac, Peruvian peppers, and pistachios.
While urushiol resides in all parts of the plant, including the roots, stem, and leaves, it also tends to sit in the oil between the cashew shell and nut inside.
Coming into contact with urushiol commonly results in allergic contact dermatitis, a delayed skin rash in humans that’s similar to the one you might experience after exposure to poison ivy.
An urushiol-induced skin rash appears as bumps or patches on the skin that are itchy, inflamed, and may have secretions, potentially even causing an intense burning sensation or localized swelling.
A 1982 report from the Centers for Disease Control and Prevention outlined how 7,500 bags of cashews containing urushiol residue were sold along the East Coast as part of a fundraiser, causing around 20% of the purchasers to experience a rash.
In an older animal study, cashew nutshell extract was fed to rats in varying amounts, resulting in a wide range of symptoms, including licking, scratching, tremors, increased pain sensitivity, mucus secretions, passive behavior, and even death.
The type and degree of reaction may depend on how much urushiol you’re exposed to and whether you consumed it or had direct skin contact with it.
Raw cashews in their shell contain urushiol, a toxin that causes a delayed allergic skin reaction similar to that caused by poison ivy. How severe your symptoms are may depend on the dose, type of contact, and how your body responds to allergens.
Roasting or steaming shelled cashews at high temperatures removes any urushiol that may have soaked through their shells and into the nuts, making them safe to consume.
This is why cashews are not sold in stores with their shells still intact, as well as why they’re typically sold roasted or otherwise heat-exposed.
Even cashews labeled as raw in stores have been shelled and heat-treated, either through roasting or steaming, to remove urushiol residue. Raw, in this sense, indicates that they have had nothing else added to them, such as salt or flavoring.
As such, you can be confident that the cashews you purchase from the store are safe to consume, as they’ve been commercially prepared to remove the naturally occurring urushiol.
Store-bought cashews have been carefully processed and prepared to remove any unwanted urushiol residue before they reach consumers. This is true even for commercially prepared cashews labeled as raw.
Cashews contain a natural toxin called urushiol in their raw, unprocessed state. The toxin is found around the cashew shell and can leach out onto the exterior of the nut itself.
If you were to handle or consume cashews in their raw form, you would likely experience a reaction similar to that caused by poison ivy, such as an itchy and inflamed skin rash that may cause a burning sensation.
However, even cashews labeled as raw at the grocery store have been shelled and heat-treated to remove any urushiol residue to prevent consumers from having this reaction.
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