Soapnuts - Botany And History
The soapnut trees are plants that grow throughout much of Asia and some parts of Europe. They are renowned since ancient times for being a source of saponin, a natural surfactant produced by some plants that can be employed in much the same way as synthetic soaps.
Historically, soap is not a 'universal invention', but rather an innovation discovered by only very few cultures in both East and West. While the rest of the world scrubbed, lathered, and languished in the luxury of primitive oil-based or fat-lye-and-tallow based soaps, some cultures employed a more natural and wholesome means to clean their persons and articles of clothing – namely, the use of plant matter that is known to contain a very strong concentration of saponin. For the Native Americans, this could be anything from yucca roots, cassava roots, or soapberries, while in India, Japan, and some parts of China, it was the soapnut. Islands such as the Philippines would employ a saponin-filled vine called gugo (St Thomas bean), while other cultures who have yet to discover soap relied on plant-based cleaners.
Despite the prolific number of natural surfactants, soapnuts rank as among the most well-known, most commonly employed, and most popular, at least in the western world. The soapnut tree (either S. mukorossi, or S. trifolatus) thrives in semi-tropical to somewhat cool environments and prefers loamy to slightly clayey soils. These can grow to as tall as sixteen feet, or more. Despite its being called the 'soapnut' tree, it is not actually its nuts that are used as natural soap – as it hasn't any! – but rather the collected and dried fruits of the plant which is marketed as such.
The soapnut tree is characterised not only by its thick umbrella-like covering of leaves, but for its heavy, close-grained, yellow-hued wood and small, jade-hued flowers. The fruits of the soapnut tree, from which soapnuts (really the seed of the tree along with its fruit) is derived, is lime-green in colour, with a fleshy, yet smooth skin when unripe, yet quickly becomes yellowish-brown when ripe.  Despite being chiefly used for soapmaking purposes, the wood of the soapnut tree also serves a purpose, although of the non-medicinal kind.
Soapnuts - Herbal Uses
Soapmaking aside, the wood from the soapnut tree is usually employed a construction material or firewood due to its density, hardness, and beautiful grain. This use is but a secondary facet that pales in comparison to the primary purpose of soapnut trees, which are to bear fruit that can be collected and dried to be used as soapnuts. 
The fruits of the tree itself are its most popular product, sold whole, crushed, or powdered (but always in dried form) to be used as natural surfactant for everything ranging from cosmetics, to laundry, to general household cleaning. Soapnuts, called reetha in several parts of India as well as in the West (although the latter only holds true among Ayurvedic practitioners and alternative-cosmetic junkies) is popularly sold both whole and in powder form as a natural shampoo, usually mixed with other beneficial herbs such as shikakai and amla. The use of soapnuts is relatively simple as with all natural surfactants, as warm water and some minor agitation by rubbing or shaking a container full of its powder or whole nuts will usually aggravate it enough to form suds that, while nowhere near as sudsy as synthetic cleaners, is potent enough to clean hair, skin, and clothes, without being as harsh as synthetic soaps and shampoos. Due to this benefit, individuals who wish to go 'all-natural' with their hair-care usually try using soapnuts at least once and either stick with it, or try other alternatives. Soapnuts are believed to not only cleanse the hair and skin in Ayurvedic medicine, but also to nourish, thicken, and blacken hair. Soapnuts contain natural antiseptic and antimicrobial properties, making it useful for treating a wide assortment of skin and scalp problems, and, if used in tandem with acidic rinses and other nourishing herbs such as amla, can even be used to treat lice infection. Since soapnuts are hypoallergenic, they can be used even by individuals with very sensitive skin. Because it can easily be prepared, whole or powdered soapnuts can be used in lieu of synthetic surfactants for nearly every imaginable use beyond the cosmetic (i. e. as laundry or dish-washing soap, and even toothpaste). 
Aside from their many purposeful uses, soapnuts also possess powerful medicinal properties that have been employed in Ayurvedic medicine since ancient times. In Ayuervedic medicine, soapnut powder mixed with peppercorns and sniffed is believed to help relieve migraines and mild asthma, while powdered soapnut mixed with potassium alum and water can be used as an alternative to synthetic toothpaste, and used to treat halitosis, toothaches, gingivitis, and even dental caries. The fleshy skins of the soapnut fruits (preferably fresh ones) can also be prepared as a remedy for hemorrhoids when mixed and charred with catechu. This is then added into ghee and consumed for seven consecutive days with meals. The external part of the soapnut may also be decocted in water and drunk to help relieve diarrhea, incontinence, and a slew of urinary problems. 
Furthermore, soapnuts can also be used as an antidote for (mild) poisons, whether by creating a decoction of soapnuts which then drunk (traditionally employed to aid the recovery of opium addicts), or by macerating it in vinegar and using it as a liniment for the bite of poisonous insects. Powdered soapnuts may also be smoked, as it is traditionally believe to counteract poisons. 
The medicinal / Ayurvedic uses of soapnuts may seem a tad alien to the western herbalist, so it is advised to conduct in-depth research prior to attempting any Ayurvedic remedy sans the guidance of an experienced practitioner. It should also be noted that while soapnuts are gentle surfactants, like the St Thomas bean, one should avoid exposing the eyes to soapnut suds, as it can be very uncomfortable and may cause an allergic reaction.
Names of Soapnuts, Past and Present
Hindu / Panjabi: reetha
Sanskrit: arishthaka / raktebeeja
Pharasi: phantuk pharasi
English: soapnuts / soapberry / areetha (adapted from Indian) / reetha (adapted from Indian)
Latin (scientific nomenclature): Sapindus mukorossi Gaer. / Sapindus trifoliatus Linn. (two of the most commonly employed species of soapnuts)
Main article researched and created by Alexander Leonhardt,
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