Aloe vera, pronounced /ˈæloʊ ˈvɪrə/[1], also known as the true aloe or medicinal aloe, is a species of succulent plant in the genus Aloe that is believed to have originated in the Sudan[citation needed]. Aloe vera grows in arid climates and is widely distributed in Africa, India, Nepal and other arid areas.[citation needed]
The species is frequently cited as being used in herbal medicine. Many scientific studies on the use of extracts of Aloe vera have been undertaken, some of them conflicting.[2][3][4][5]
Despite these limitations, there is some preliminary evidence that Aloe vera extracts may be useful in the treatment of wound and burn healing, minor skin infections, sebaceous cysts, diabetes, and elevated blood lipids in humans.[4] These positive effects are thought to be due to the presence of compounds such as polysaccharides, mannans, anthraquinones, and lectins.[4][6][7]
Despite these limitations, there is some preliminary evidence that Aloe vera extracts may be useful in the treatment of wound and burn healing, minor skin infections, sebaceous cysts, diabetes, and elevated blood lipids in humans.[4] These positive effects are thought to be due to the presence of compounds such as polysaccharides, mannans, anthraquinones, and lectins.[4][6][7]
Description
Aloe vera is a stemless or very short-stemmed succulent plant growing to 60–100 cm (24–39 in) tall,spreading by offsets. The leaves are thick and fleshy, green to grey-green, with some varieties showing white flecks on the upper and lower stem surfaces.[8] The margin of the leaf is serrated and has small white teeth. The flowers are produced in summer on a spike up to 90 cm (35 in) tall, each flower pendulous, with a yellow tubular corolla 2–3 cm (0.8–1.2 in) long.[8][9] Like other Aloe species, Aloe vera forms arbuscular mycorrhiza, a symbiosis that allows the plant better access to mineral nutrients in soil.[10]
Aloe vera is a stemless or very short-stemmed succulent plant growing to 60–100 cm (24–39 in) tall,spreading by offsets. The leaves are thick and fleshy, green to grey-green, with some varieties showing white flecks on the upper and lower stem surfaces.[8] The margin of the leaf is serrated and has small white teeth. The flowers are produced in summer on a spike up to 90 cm (35 in) tall, each flower pendulous, with a yellow tubular corolla 2–3 cm (0.8–1.2 in) long.[8][9] Like other Aloe species, Aloe vera forms arbuscular mycorrhiza, a symbiosis that allows the plant better access to mineral nutrients in soil.[10]
Taxonomy and etymology
Spotted forms of Aloe vera are sometimes known as Aloe vera var. chinensis.
The species has a number of synonyms: A. barbadensis Mill., Aloe indica Royle, Aloe perfoliata L. var. vera and A. vulgaris Lam.,[11][12] and common names including Chinese Aloe, Indian Aloe, true Aloe, Barbados Aloe, burn Aloe, first aid plant.[9][13][14][15][16] The species name vera means "true" or "genuine."[13] Some literature identifies the white spotted form of Aloe vera as Aloe vera var. chinensis,[17][18] however, the species varies widely with regard to leaf spots [19] and it has been suggested that the spotted form of Aloe vera may be conspecific with A. massawana.[20] The species was first described by Carl Linnaeus in 1753 as Aloe perfoliata var. vera,[21] and was described again in 1768 by Nicolaas Laurens Burman as Aloe vera in Flora Indica on the 6th of April and by Philip Miller as Aloe barbadensis some ten days after Burman in the Gardener's Dictionary.[22]
Techniques based on DNA comparison suggest that Aloe vera is relatively closely related to Aloe perryi, a species that is endemic to Yemen.[23] Similar techniques, using chloroplast DNA sequence comparison and ISSR profiling have also suggested that Aloe vera is closely related to Aloe forbesii, Aloe inermis, Aloe scobinifolia, Aloe sinkatana, and Aloe striata.[24] With the exception of South African species A. striata, these Aloe species are native to Socotra (Yemen), Somalia, and Sudan.[24] The lack of obvious natural populations of the species have led some authors to suggest that Aloe vera may be of hybrid origin.[25]hi
[edit]
Distribution
The natural range of Aloe vera is unclear, as the species has been widely cultivated throughout the world. Naturalised stands of the species occur in the southern half of the Arabian peninsula, through North Africa (Morocco, Mauritania, Egypt) as well as Sudan and neighbouring countries, along with the Canary, Cape Verde, and Madeira Islands.[11] This distribution is somewhat similar to the one of Euphorbia balsamifera, Pistacia atlantica, and a few others, suggesting that a dry sclerophyl forest once covered large areas, but has been dramatically reduced due to desertification in the Sahara, leaving these few patches isolated. Several closely related species (or sometimes identical) can be found on the two extreme sides of the Sahara: Dragon trees and Aeonium being some of the most representative examples.
The species was introduced to China and various parts of southern Europe in the 17th century.[26] The species is widely naturalised elsewhere, occurring in temperate and tropical regions of Australia, Barbados, Belize, Nigeria, Paraguay and the US[19][27] It has been suggested that the actual species' distribution is the result of human cultivation and that the taxonomy could be doubtful too.[20]
[edit]
Cultivation
Aloe vera can be grown as an ornamental plant.
Aloe vera has been widely grown as an ornamental plant. The species is popular with modern gardeners as a putatively medicinal plant and due to its interesting flowers, form, and succulence. This succulence enables the species to survive in areas of low natural rainfall, making it ideal for rockeries and other low-water use gardens.[8] The species is hardy in zones 8–11, although it is intolerant of very heavy frost or snow.[9][28] The species is relatively resistant to most insect pests, though spider mites, mealy bugs, scale insects, and aphid species may cause a decline in plant health.[29][30] In pots, the species requires well-drained sandy potting soil and bright sunny conditions; however, in very hot and humid tropical or subtropical climates, aloe plants should be protected from direct sun and rain, as they will burn and/or turn mushy easily under these conditions. The use of a good-quality commercial propagation mix or pre-packaged "cacti and succulent mix" is recommended, as they allow good drainage.[31] Terracotta pots are preferable as they are porous.[31] Potted plants should be allowed to completely dry prior to re-watering. When potted aloes become crowded with "pups" growing from the sides of the "mother plant," they should be divided and re-potted to allow room for further growth and help prevent pest infestations. During winter, Aloe vera may become dormant, during which little moisture is required. In areas that receive frost or snow, the species is best kept indoors or in heated glasshouses.[9] Large scale agricultural production of Aloe vera is undertaken in Australia,[32] Bangladesh, Cuba,[33] the Dominican Republic, China, Mexico,[34] India,[35] Jamaica,[36] Kenya and South Africa,[37] along with the USA[38] to supply the cosmetics industry with Aloe vera gel.
[edit]
Uses
[edit]
Claims of medical properties
Aloe vera gel being used to make a dessert.
Scientific evidence for the cosmetic and therapeutic effectiveness of aloe vera is limited and when present is frequently contradictory.[2][3] Despite this, the cosmetic and alternative medicine industries regularly make claims regarding the soothing, moisturizing, and healing properties of aloe vera, especially via Internet advertising.[4][39][40][41][42] Aloe vera gel is used as an ingredient in commercially available lotions, yogurt, beverages, and some desserts.[43][44][45]
Aloe vera juice is used for consumption and relief of digestive issues such as heartburn and irritable bowel syndrome, although it bears significant potential to be toxic when taken orally.[46] It is common practice for cosmetic companies to add sap or other derivatives from Aloe vera to products such as makeup, tissues, moisturizers, soaps, sunscreens, incense, shaving cream, and shampoos.[43] Other uses for extracts of aloe vera include the dilution of semen for the artificial fertilization of sheep,[47] use as fresh food preservative,[48] and use in water conservation in small farms.[49] The supposed therapeutic uses of Aloe vera are not exclusive to the species and may be found to a lesser or greater degree in the gels of all aloes, and indeed are shared with large numbers of plants belonging to the family Asphodelaceae. Bulbine frutescens, for example, is used widely for the treatment of burns and a host of skin afflictions.[50]
Aloe vera has a long association with herbal medicine, although it is not known when its medical applications were first suspected. Early records of Aloe vera use appear in the Ebers Papyrus from 16th century BC,[16] in both Dioscorides' De Materia Medica and Pliny the Elder's Natural History written in the mid-first century CE[16] along with the Juliana Anicia Codex produced in 512 AD.[43] Aloe vera is non-toxic, with no known side effects, provided the aloin has been removed by processing. Taking aloe vera that contains aloin in excess amounts has been associated with various side-effects.[4][5][51] However, the species is used widely in the traditional herbal medicine of China, Japan, Russia, South Africa, the United States, Jamaica, Latin America and India.[4]
Aloe vera may be effective in treatment of wounds.[5] Evidence on the effects of its sap on wound healing, however, is limited and contradictory.[5] Some studies, for example, show that aloe vera promotes the rates of healing,[52][53] while, in contrast, other studies show that wounds to which aloe vera gel was applied were significantly slower to heal than those treated with conventional medical preparations.[54][55] A more recent review (2007) concludes that the cumulative evidence supports the use of aloe vera for the healing of first to second degree burns.[56] In addition to topical use in wound or burn healing, internal intake of aloe vera has been linked in preliminary research with improved blood glucose levels in diabetics,[57][58] and with lower blood lipids in hyperlipidaemic patients,[59] but also with acute hepatitis (liver disease).[51] In other diseases, preliminary studies have suggested oral aloe vera gel may reduce symptoms and inflammation in patients with ulcerative colitis.[60] Compounds extracted from aloe vera have been used as an immunostimulant that aids in fighting cancers in cats and dogs;[6] however, this treatment has not been scientifically tested in humans.
Topical application of aloe vera may be effective for genital herpes and psoriasis.[61] However, it is not effective for the prevention of radiation-induced injuries. Although anecdotally useful, it has not been proven to offer protection from sunburn or suntan.[62] In a double-blind clinical trial, both the group using an aloe vera containing dentifrice and the group using a fluoridated dentifrice had a reduction of gingivitis and plaque, but no statistically significant difference was found between the two.[63]
Aloe vera extracts might have antibacterial and antifungal activities, which possibly could help treat minor skin infections, such as boils and benign skin cysts and may inhibit growth of fungi causing tinea.[64] For bacteria, inner-leaf gel from aloe vera was shown in one study to inhibit growth of Streptococcus and Shigella species in vitro.[65] In contrast, aloe vera extracts failed to show antibiotic properties against Xanthomonas species.[66]
[edit]
Commodity uses
Aloe vera is now widely used on facial tissues, where it is promoted as a moisturiser and/or anti-irritant to reduce chafing of the nose of users suffering hay-fever or cold.[67] It has also been suggested that biofuels could be obtained from Aloe vera seeds.[68] It can also be used to retwist dreadlocked hair, a favourite agent for vegans and those preferring natural products. Aloe vera is also used for soothing the skin, and keeping the skin moist to help avoid flaky scalp and skin in harsh and dry weather. Aloe vera may also be used as a moisturizer for oily skin.
[edit]
Historical uses
Aloin was the common ingredient in over-the-counter (OTC) laxative products in the United States prior to 2003, when the Food and Drug Administration ruled that aloin was a class III ingredient, thereby banning its use.[69] It should be noted that unprocessed aloe that contains aloin is used primarily as a laxative, whereas processed Aloe vera juice that does not contain significant amounts of aloin is used as a digestive healer. Manufacturers commonly remove aloin in processing due to the FDA ruling.
[edit]
Culinary uses
Aloe is also used as a food substance. Some molecular gastronomists have begun to take advantage of its gelling properties. Perhaps the most notable among these is Chef Quique Dacosta's "Oysters Guggenheim," created at El Poblet in Spain.[70]
[edit]
Side Effects and Cautions
Use of topical aloe vera is not associated with significant side effects. A 2-year National Toxicology Program (NTP) study on oral consumption of non-decolorized whole leaf extract of aloe vera found clear evidence of carcinogenic activity in male and female rats, based on tumors of the large intestine. According to the NTP, from what is known right now there is nothing that would lead them to believe that these findings are not relevant to humans. However, more information, including how individuals use different types of aloe vera products, is needed to determine the potential risks to humans. Abdominal cramps and diarrhea have been reported with oral use of aloe vera. Diarrhea, caused by the laxative effect of oral aloe vera, can decrease the absorption of many drugs. People with diabetes who use glucose-lowering medication should be cautious if also taking aloe by mouth because preliminary studies suggest aloe may lower blood glucose levels. There have been a few case reports of acute hepatitis from aloe vera taken orally. However, the evidence is not definitive.[71]
[edit]
Biologically active compounds
Aloe vera leaves contain a range of biologically active compounds, the best-studied being acetylated mannans, polymannans, anthraquinone C-glycosides, anthrones and anthraquinones, and various lectins.[4][6][7]
Spotted forms of Aloe vera are sometimes known as Aloe vera var. chinensis.
The species has a number of synonyms: A. barbadensis Mill., Aloe indica Royle, Aloe perfoliata L. var. vera and A. vulgaris Lam.,[11][12] and common names including Chinese Aloe, Indian Aloe, true Aloe, Barbados Aloe, burn Aloe, first aid plant.[9][13][14][15][16] The species name vera means "true" or "genuine."[13] Some literature identifies the white spotted form of Aloe vera as Aloe vera var. chinensis,[17][18] however, the species varies widely with regard to leaf spots [19] and it has been suggested that the spotted form of Aloe vera may be conspecific with A. massawana.[20] The species was first described by Carl Linnaeus in 1753 as Aloe perfoliata var. vera,[21] and was described again in 1768 by Nicolaas Laurens Burman as Aloe vera in Flora Indica on the 6th of April and by Philip Miller as Aloe barbadensis some ten days after Burman in the Gardener's Dictionary.[22]
Techniques based on DNA comparison suggest that Aloe vera is relatively closely related to Aloe perryi, a species that is endemic to Yemen.[23] Similar techniques, using chloroplast DNA sequence comparison and ISSR profiling have also suggested that Aloe vera is closely related to Aloe forbesii, Aloe inermis, Aloe scobinifolia, Aloe sinkatana, and Aloe striata.[24] With the exception of South African species A. striata, these Aloe species are native to Socotra (Yemen), Somalia, and Sudan.[24] The lack of obvious natural populations of the species have led some authors to suggest that Aloe vera may be of hybrid origin.[25]hi
[edit]
Distribution
The natural range of Aloe vera is unclear, as the species has been widely cultivated throughout the world. Naturalised stands of the species occur in the southern half of the Arabian peninsula, through North Africa (Morocco, Mauritania, Egypt) as well as Sudan and neighbouring countries, along with the Canary, Cape Verde, and Madeira Islands.[11] This distribution is somewhat similar to the one of Euphorbia balsamifera, Pistacia atlantica, and a few others, suggesting that a dry sclerophyl forest once covered large areas, but has been dramatically reduced due to desertification in the Sahara, leaving these few patches isolated. Several closely related species (or sometimes identical) can be found on the two extreme sides of the Sahara: Dragon trees and Aeonium being some of the most representative examples.
The species was introduced to China and various parts of southern Europe in the 17th century.[26] The species is widely naturalised elsewhere, occurring in temperate and tropical regions of Australia, Barbados, Belize, Nigeria, Paraguay and the US[19][27] It has been suggested that the actual species' distribution is the result of human cultivation and that the taxonomy could be doubtful too.[20]
[edit]
Cultivation
Aloe vera can be grown as an ornamental plant.
Aloe vera has been widely grown as an ornamental plant. The species is popular with modern gardeners as a putatively medicinal plant and due to its interesting flowers, form, and succulence. This succulence enables the species to survive in areas of low natural rainfall, making it ideal for rockeries and other low-water use gardens.[8] The species is hardy in zones 8–11, although it is intolerant of very heavy frost or snow.[9][28] The species is relatively resistant to most insect pests, though spider mites, mealy bugs, scale insects, and aphid species may cause a decline in plant health.[29][30] In pots, the species requires well-drained sandy potting soil and bright sunny conditions; however, in very hot and humid tropical or subtropical climates, aloe plants should be protected from direct sun and rain, as they will burn and/or turn mushy easily under these conditions. The use of a good-quality commercial propagation mix or pre-packaged "cacti and succulent mix" is recommended, as they allow good drainage.[31] Terracotta pots are preferable as they are porous.[31] Potted plants should be allowed to completely dry prior to re-watering. When potted aloes become crowded with "pups" growing from the sides of the "mother plant," they should be divided and re-potted to allow room for further growth and help prevent pest infestations. During winter, Aloe vera may become dormant, during which little moisture is required. In areas that receive frost or snow, the species is best kept indoors or in heated glasshouses.[9] Large scale agricultural production of Aloe vera is undertaken in Australia,[32] Bangladesh, Cuba,[33] the Dominican Republic, China, Mexico,[34] India,[35] Jamaica,[36] Kenya and South Africa,[37] along with the USA[38] to supply the cosmetics industry with Aloe vera gel.
[edit]
Uses
[edit]
Claims of medical properties
Aloe vera gel being used to make a dessert.
Scientific evidence for the cosmetic and therapeutic effectiveness of aloe vera is limited and when present is frequently contradictory.[2][3] Despite this, the cosmetic and alternative medicine industries regularly make claims regarding the soothing, moisturizing, and healing properties of aloe vera, especially via Internet advertising.[4][39][40][41][42] Aloe vera gel is used as an ingredient in commercially available lotions, yogurt, beverages, and some desserts.[43][44][45]
Aloe vera juice is used for consumption and relief of digestive issues such as heartburn and irritable bowel syndrome, although it bears significant potential to be toxic when taken orally.[46] It is common practice for cosmetic companies to add sap or other derivatives from Aloe vera to products such as makeup, tissues, moisturizers, soaps, sunscreens, incense, shaving cream, and shampoos.[43] Other uses for extracts of aloe vera include the dilution of semen for the artificial fertilization of sheep,[47] use as fresh food preservative,[48] and use in water conservation in small farms.[49] The supposed therapeutic uses of Aloe vera are not exclusive to the species and may be found to a lesser or greater degree in the gels of all aloes, and indeed are shared with large numbers of plants belonging to the family Asphodelaceae. Bulbine frutescens, for example, is used widely for the treatment of burns and a host of skin afflictions.[50]
Aloe vera has a long association with herbal medicine, although it is not known when its medical applications were first suspected. Early records of Aloe vera use appear in the Ebers Papyrus from 16th century BC,[16] in both Dioscorides' De Materia Medica and Pliny the Elder's Natural History written in the mid-first century CE[16] along with the Juliana Anicia Codex produced in 512 AD.[43] Aloe vera is non-toxic, with no known side effects, provided the aloin has been removed by processing. Taking aloe vera that contains aloin in excess amounts has been associated with various side-effects.[4][5][51] However, the species is used widely in the traditional herbal medicine of China, Japan, Russia, South Africa, the United States, Jamaica, Latin America and India.[4]
Aloe vera may be effective in treatment of wounds.[5] Evidence on the effects of its sap on wound healing, however, is limited and contradictory.[5] Some studies, for example, show that aloe vera promotes the rates of healing,[52][53] while, in contrast, other studies show that wounds to which aloe vera gel was applied were significantly slower to heal than those treated with conventional medical preparations.[54][55] A more recent review (2007) concludes that the cumulative evidence supports the use of aloe vera for the healing of first to second degree burns.[56] In addition to topical use in wound or burn healing, internal intake of aloe vera has been linked in preliminary research with improved blood glucose levels in diabetics,[57][58] and with lower blood lipids in hyperlipidaemic patients,[59] but also with acute hepatitis (liver disease).[51] In other diseases, preliminary studies have suggested oral aloe vera gel may reduce symptoms and inflammation in patients with ulcerative colitis.[60] Compounds extracted from aloe vera have been used as an immunostimulant that aids in fighting cancers in cats and dogs;[6] however, this treatment has not been scientifically tested in humans.
Topical application of aloe vera may be effective for genital herpes and psoriasis.[61] However, it is not effective for the prevention of radiation-induced injuries. Although anecdotally useful, it has not been proven to offer protection from sunburn or suntan.[62] In a double-blind clinical trial, both the group using an aloe vera containing dentifrice and the group using a fluoridated dentifrice had a reduction of gingivitis and plaque, but no statistically significant difference was found between the two.[63]
Aloe vera extracts might have antibacterial and antifungal activities, which possibly could help treat minor skin infections, such as boils and benign skin cysts and may inhibit growth of fungi causing tinea.[64] For bacteria, inner-leaf gel from aloe vera was shown in one study to inhibit growth of Streptococcus and Shigella species in vitro.[65] In contrast, aloe vera extracts failed to show antibiotic properties against Xanthomonas species.[66]
[edit]
Commodity uses
Aloe vera is now widely used on facial tissues, where it is promoted as a moisturiser and/or anti-irritant to reduce chafing of the nose of users suffering hay-fever or cold.[67] It has also been suggested that biofuels could be obtained from Aloe vera seeds.[68] It can also be used to retwist dreadlocked hair, a favourite agent for vegans and those preferring natural products. Aloe vera is also used for soothing the skin, and keeping the skin moist to help avoid flaky scalp and skin in harsh and dry weather. Aloe vera may also be used as a moisturizer for oily skin.
[edit]
Historical uses
Aloin was the common ingredient in over-the-counter (OTC) laxative products in the United States prior to 2003, when the Food and Drug Administration ruled that aloin was a class III ingredient, thereby banning its use.[69] It should be noted that unprocessed aloe that contains aloin is used primarily as a laxative, whereas processed Aloe vera juice that does not contain significant amounts of aloin is used as a digestive healer. Manufacturers commonly remove aloin in processing due to the FDA ruling.
[edit]
Culinary uses
Aloe is also used as a food substance. Some molecular gastronomists have begun to take advantage of its gelling properties. Perhaps the most notable among these is Chef Quique Dacosta's "Oysters Guggenheim," created at El Poblet in Spain.[70]
[edit]
Side Effects and Cautions
Use of topical aloe vera is not associated with significant side effects. A 2-year National Toxicology Program (NTP) study on oral consumption of non-decolorized whole leaf extract of aloe vera found clear evidence of carcinogenic activity in male and female rats, based on tumors of the large intestine. According to the NTP, from what is known right now there is nothing that would lead them to believe that these findings are not relevant to humans. However, more information, including how individuals use different types of aloe vera products, is needed to determine the potential risks to humans. Abdominal cramps and diarrhea have been reported with oral use of aloe vera. Diarrhea, caused by the laxative effect of oral aloe vera, can decrease the absorption of many drugs. People with diabetes who use glucose-lowering medication should be cautious if also taking aloe by mouth because preliminary studies suggest aloe may lower blood glucose levels. There have been a few case reports of acute hepatitis from aloe vera taken orally. However, the evidence is not definitive.[71]
[edit]
Biologically active compounds
Aloe vera leaves contain a range of biologically active compounds, the best-studied being acetylated mannans, polymannans, anthraquinone C-glycosides, anthrones and anthraquinones, and various lectins.[4][6][7]
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