Neem is an evergreen tree which is endemic to the Indian subcontinent and has been introduced to many other areas in the tropics. Neem oil is a vegetable oil pressed from the fruits and seeds of the neem. It is the most important of the commercially available products of neem for organic farming and medicines.
Neem oil varies in color; it can be golden yellow, yellowish brown, reddish brown, dark brown, greenish brown, or bright red. It has a rather strong odor that is said to combine the odours of peanut and garlic. It is composed mainly of triglycerides and contains many triterpenoid compounds, which are responsible for the bitter taste.
Azadirachtin is the most well known and studied triterpenoid in neem oil. Nimbin is another triterpenoid which has been credited with some of neem oil’s properties as an antiseptic, antifungal, antipyretic and antihistamine. Neem oil also contains several sterols, including campesterol, beta-sitosterol, and stigmasterol.
The method of processing is likely to affect the composition of the oil, since the methods used, such as pressing (expelling) or solvent extraction are unlikely to remove exactly the same mix of components in the same proportions. The neem oil yield that can be obtained from neem seed kernels also varies widely in literature from 25% to 45%.
The oil can be obtained through pressing (crushing) of the seed kernel both through cold pressing or through a process incorporating temperature controls 40 to 50 °C. Neem seed oil can also be obtained by solvent extraction of the neem seed, fruit, oil, cake or kernel. A large industry in India extracts the oil remaining in the seed cake using hexane. This oil is of a lower quality as compared to the cold pressed oil and is mostly used for soap manufacturing. Neem cake is a by-product obtained in the solvent extraction process for neem oil.
Neem oil is not used for cooking purposes. In India, it is used for preparing cosmetics such as soaps, hair products, body hygiene creams, hand creams.
Neem oil has an extensive history of traditional human use in India and surrounding regions for a variety of therapeutic purposes. Ayurvedic uses of neem include the treatment of acne, fever, leprosy, malaria, ophthalmia and tuberculosis. Various folk remedies for neem include use as an anthelmintic, antifeedant, antiseptic, diuretic, emmenagogue, contraceptive, febrifuge, parasiticide, pediculocide, and insecticide, and for the treatment of tetanus, urticaria, eczema, scrofula and erysipelas.
Formulations made of neem oil also find wide usage as a biopesticide for organic farming, as it repels a wide variety of pests including the mealy bug, beet armyworm, aphids, the cabbage worm, thrips, whiteflies, mites, fungus gnats, beetles, moth larvae, mushroom flies, leafminers, caterpillars, locust, nematodes and the Japanese beetle. Neem oil is not known to be harmful to mammals, birds, earthworms or some beneficial insects such as butterflies, honeybees and ladybirds (ladybugs in US English) if it is not concentrated directly into their area of habitat or on their food source. It can be used as a household pesticide for ant, bedbug, cockroach, housefly, sand fly, snail, termite and mosquitoes both as repellent and larvicide. Neem oil also controls black spot, powdery mildew, anthracnose and rust fungi.
Neem extracts act as a phagorepellent (antifeedant) and by blocking the action of the insect molting hormone ecdysone. Azadirachtin is the most active of these growth regulators , occurring at 0.2–0.4 % in the neem seeds.
Neem oil and other neem products should not be consumed by pregnant women, women trying to conceive, or children.
There is some evidence that ingestion of neem oil may be associated with liver damage in children.
Several case reports detail severe toxicity associated with ingestion of neem oil. In one case, ingestion of 20ml was sufficient to cause vomiting, convulsions, and toxic encephalopathy.