Cashew Nut Oil – Cashews are one of the most beloved nuts worldwide. Despite the fact that they are the third most popular nut in terms of consumption, we are not acquainted with its nut oil. The lack of attention paid to cashew nut oil and its obscurity from global markets is astonishing. Nonetheless, cashews are oily nuts, and they yield edible oil, which, as we shall see, provides significant benefits for skin conditioning and turns out to be good cooking oil. However, cashews shells yield a different oil, called the Cashew Nut Shell Oil (trade name CNSL), which is incredibly toxic and is used mostly in industrial applications. To us, cashew nut oil evokes the greatest interest.
The cashew tree is the Anacardium occidentale, a unique tree that is evergreen and is native to the rainforests of Brazil. It was spread to other countries, like India and Ivory Coast, by Portuguese colonial settlers. Now, it is grown in many countries that provide a suitable climate for an evergreen tree to grow, mainly in the tropical belt. Outside this region, Italy is a major producer of cashew nuts lying in the Mediterranean climatic belt. Contrary to popular belief, more than 90% of the cashew production is still from wild trees; only the rest is from plantations. 
Cashew nuts hang out of the ripe fruit, which is called the cashew apple. It is one of the weirdest looking nuts out there. Cashew apples are generally used to make fermented drinks in local cultures, whereas cashews are used in confectioneries, cuisines and also turned into cashew butter.
These nuts are rarely turned into edible oil because of probably low demand for the oil, and that much of the nuts (even the broken ones) are readily used in confectioneries. But the oil holds promising health benefits.
Colour and Aroma
Most of the oils available are solvent extracted oils (mainly by n-hexane). These are dull yellowish. But the oil tastes sweet without much odour. Cold-pressed virgin oils may have a slightly better taste and aroma. However, it is a shame that there is hardly any commercial production of it.
Cashew nut oil can provide certain specific therapeutic benefits when applied directly to the skin.
- Emollient – Very high concentration of oleic acid lends it the property of being a powerful emollient. It thus acts as a brilliant moisturizer.
- Mild anti-inflammatory – A small yet sizeable percentage of the oil is made of omega-6 fatty acid, an essential fatty acid because it helps regulate the inflammatory reactions in our body. Thus, cashew nut oil could be used on skin conditions that rely on causing inflammation and making the skin red and swollen and painful.
Uses and Health Benefits
As compared to a much more popular nut oil, like almond oil, about which we know a lot, both from traditional uses of the sweet almond oil in various civilizations to the validations of some of those traditional uses by modern medical science, we are flummoxed at the lack of such information about cashew nut’s edible oil. One of the possible reasons for this could be that the shell oil of cashew is quite toxic (similar to poison ivy). People of ancient times might have experienced contact dermatitis when the shell oil somehow got into the cashew kinds of butter or the oils (if at all they expelled it). That could probably have deterred the ancients from using the oil of the cashew.
However, our present extraction methods and careful quality control in harvesting have made things much better. There are few cases of people getting contact dermatitis from eating cashews, and hence the oils made from these clean cashews would not be contaminated with toxic compounds of the shell oil. Accordingly, we can explore the potential benefits of this oil for our skin and cooking.
Cashew Nut Oil for the Skin
The oil has a low viscosity, which means that it spreads easily. It helps prevent moisture from escaping our skin because of the skin barrier enhancement provided by the fatty acids in it, chief among them being oleic acid . Cashew nut oil can be used as a light skin conditioner to keep the skin smooth and prevent cracks that develop due to dry, cold weather.
It has a small amount of vitamin E, which helps keep the skin nourished and fights free radicals, keeping the skin taut, thus reducing the signs of ageing. However, the potency of such anti-ageing action depends on the quantity of Vitamin E supplied by the oil and how readily it gets absorbed into our cells from topical applications. The latter also depends on the quality of Vitamin E (whether it is mainly in tocopherols or tocotrienols, the two forms of Vitamin E). However, we can rest assured that it does bring some anti-ageing properties to the table. As we shall note in the nutrition section of this article, cashew oil contains the gamma-tocopherol form of Vitamin E, which is somewhat rare to find among oils, and we shall see its unique health benefits.
The presence of linoleic acid (an omega-6 fatty acid) would make it suitable for use in inflammation dependent skin conditions, like acne vulgaris, psoriasis, eczema and even minor insect bites and rashes. This is because linoleic acid helps synthesize some prostaglandins that are a kind of lipids (fats) that help reduce inflammation by dilating our veins. 
As a cooking oil
The suitability of cashew nut oil for cooking purposes has not been evaluated. Still, it has the right proportions of saturated to unsaturated fats to make it a good cooking oil. It does possess a good shelf life because of the low oxidation rates of oleic acid. In a way, it is similar to olive oil. An old study notes that cashew oil is suitable for frying stuff too. 
Nutritional and Medicinal Information
The first major thing to note about any edible oil is its composition of fatty acids.
|Fatty acid||Carbon notation||Composition|
|Oleic Acid||C 18:1||68 – 80 %|
|Linoleic Acid||C 18:2||0 – 21 %|
|Palmitic Acid||C 16:0||4 – 17 %|
|Stearic Acid||C 18:0||1 – 11 %|
Oleic acid (which is a monounsaturated fatty acid MUFA) is the major constituent of the oil of cashew kernels. It provides oil protection from going rancid. Linoleic acid, as we know, is a polyunsaturated fatty acid (PUFA). Still, more importantly, it is an essential fatty acid, in the sense that in the absence of this oil in our diet, we develop deficiency diseases. We cannot go without linoleic acid in our life. Plus, it is linked to pathways that reduce inflammation in our body, though not as powerful as gamma-linolenic acid (an omega-3). 
However, it is to be noted that the composition of fatty acids in cashew oil seems to vary a lot. Take, for example, the case of linoleic acid, whose percentage lies from a lower value of 0% to even upto 20% of the oil’s total weight. These are not explained and is difficult to explain based on minor variations in cashews sourced from different continents viz South America (a cashew producer like Brazil), Africa (like Nigeria) and Asia (the major producer is India). This needs to be looked into by researchers.
Another essential set of parameters of any oil is its physico-chemical properties.
|Peroxide Value||10.7 mg KOH/g|
|Saponification Value||137 mg KOH/g|
|Iodine Value||41.3 mg I2/100g|
It has a lower density than water, is light and spreads well and does not dry out quickly.
Apart from the fatty acids, cashew kernel oil also contains small amounts of sterols. These are similar to cholesterol, but since they are derived from plants, they are called phytosterols. They have been linked to reducing cholesterol by slowing down its absorption in the intestines . But, since we don’t know the exact compositions of sterols in cashew nut oil, it is impossible to comment on how much cholesterol reduction this oil may provide is used as cooking oil or just used for drizzling on the salads.
Cashew nut oil has been documented to contain gamma-tocopherol (about 40 – 80 mg per 100gm of oil) , which is unique as most foods are rich in the alpha form of tocopherol. Vitamin E is a fat-soluble vitamin, and it has a dominant role in reducing inflammation and neurodegenerative diseases because it is a potent antioxidant. A widely cited study conducted by the University of Berkeley noted that gamma-tocopherol inhibits reactive nitrogen species (a class of free radicals that work similar to reactive oxygen species and damage our cells daily). These species are higher in areas with higher vehicular pollution. So, people living in such cities may opt for oil with higher gamma-tocopherol. Apart from cashew oil, corn and soybean oil are also good providers of this form of Vit. E. 
Side Effects, Safe Dosage and Toxicity Issues
There is the absence of material safety data sheets regarding cashew nut oil. However, cashew nuts have been known to cause contact dermatitis . But, these cases are becoming rarer and rarer.
Cashew Nut Shell Liquid (CNSL)
The natural resin found between the outer shell of the cashew, and its nut is extracted (not cold-pressed but using solvents) and called the cashew nut shell liquid. It is a brownish liquid that dries quickly. It is a famed reactant in many chemical reactants in some industrial applications, especially to make polymers. Plus, it is also used to make paints and in friction-reducing coatings. However, we shall delve into its applications for health and household.
CNSL to counter the dengue spreading mosquito A. aegypti
The compounds present in CNSL have shown the ability to kill the larvae of the Aedes aegypti mosquito. The females of this species are the vectors (carriers) of the dengue virus, which causes sharp fever and a host of other symptoms. Dengue fever is a common but dangerous fever in rainy, humid, tropical climates. Add a few drops of cashew nut shell oil to a litre of castor oil and mix it properly. Pour some drops into stored water (like in desert coolers) and in stagnant water, like out in the garden where puddles may form will kill the larvae of this mosquito, thus reducing the chances of catching an infectious bite. 
Note of caution: CNSL is a toxic liquid and is known to cause dermatitis similar to poison ivy when it touches the skin. Hence, use lab-grade gloves when handling this liquid.
Moreover, a bulk of research has identified that CNSL has anti-bacterial action, anti-tumour properties and is also an antioxidant (because of phenolic constituents like cardanol and cardol). But this oil can neither be ingested nor applied topically. Biotechnological innovations are coming up to make use of its constituents in medicines by eliminating the toxic portion.
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- Essential Fatty Acids and Skin Health. Linus Pauling Institute at the Oregon State University.
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- Akinhanmi et al. Chemical Composition and Physico-chemical properties of Cashew nut (Anacardiumoccidentale ) oil and Cashew nut shell liquid. Journal of Agricultural, Food and Environment Science.
- Ostlund RE. Inhibition of cholesterol absorption by phytosterol replete wheat germ compared with phytosterol depleted wheat germ. American Journal of Clinical Nutrition.
- Gamma-tocopherol traps mutagenic electrophiles such as NO(X) and complements alpha-tocopherol: physiological implications. Christen S et al. Proceedings of the National Academy of Sciences, USA.
- Cashew Nut dermatitis. Rosen T andFordiceDB. Southern Medical Journal.
- The mixture of cashew nut shell liquid and castor oil results in an efficient larvicide against Aedes aegypti that does not alter embryo-fetal development, reproductive performance or DNA integrity. Vani et al.
- Anacardic Acid Constituents from Cashew Nut Shell Liquid: NMR Characterization and the Effect of Unsaturation on Its Biological Activities. Morais et al.