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Aloe vera

Aloe vera (/ˈæloʊiː/ or /ˈæloʊ/) is a succulent plant species. The species is frequently cited as being used in herbal medicine since the beginning of the first century AD. Extracts from Aloe vera are widely used in the cosmetics and alternative medicine industries, being marketed as variously having rejuvenating, healing, or soothing properties. There is, however, little scientific evidence of the effectiveness or safety of Aloe vera extracts for either cosmetic or medicinal purposes, and what positive evidence is available[3] is frequently contradicted by other studies.[4][5][6]

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Aloe vera plant with flower detail inset
Scientific classification Edit this classification
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Species: Template:Taxon infoTemplate:Taxon italics
Binomial name
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Synonyms[1][2]
  • Aloe barbadensis Mill.
  • Aloe barbadensis var. chinensis Haw.
  • Aloe chinensis (Haw.) Baker
  • Aloe elongata Murray
  • Aloe flava Pers.
  • Aloe indica Royle
  • Aloe lanzae Tod.
  • Aloe maculata Forssk. (illegitimate)
  • Aloe perfoliata var. vera L.
  • Aloe rubescens DC.
  • Aloe variegata Forssk. (illegitimate)
  • Aloe vera Mill. (illegitimate)
  • Aloe vera var. chinensis (Haw.) A. Berger
  • Aloe vera var. lanzae Baker
  • Aloe vera var. littoralis J.Koenig ex Baker
  • Aloe vulgaris Lam.
Aloe vera - MHNT

Description

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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 their upper and lower stem surfaces.[7] 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 being pendulous, with a yellow tubular corolla 2–3 cm (0.8–1.2 in) long.[7][8] Like other Aloe species, Aloe vera forms arbuscular mycorrhiza, a symbiosis that allows the plant better access to mineral nutrients in soil.[9]

Aloe vera leaves contain phytochemicals under study for possible bioactivity, such as acetylated mannans, polymannans, anthraquinone C-glycosides, anthrones, other anthraquinones, such as emodin, and various lectins.[3][10][11]

Taxonomy and etymology

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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.[12][13] Common names include Chinese Aloe, Indian Aloe, True Aloe, Barbados Aloe, Burn Aloe, First Aid Plant.[8][14][15][16][17] The species epithet vera means "true" or "genuine".[14] Some literature identifies the white-spotted form of Aloe vera as Aloe vera var. chinensis;[18][19] however, the species varies widely with regard to leaf spots[20] and it has been suggested that the spotted form of Aloe vera may be conspecific with A. massawana.[21] The species was first described by Carl Linnaeus in 1753 as Aloe perfoliata var. vera,[22] and was described again in 1768 by Nicolaas Laurens Burman as Aloe vera in Flora Indica on 6 April and by Philip Miller as Aloe barbadensis some ten days after Burman in the Gardener's Dictionary.[23]

Techniques based on DNA comparison suggest Aloe vera is relatively closely related to Aloe perryi, a species endemic to Yemen.[24] Similar techniques, using chloroplast DNA sequence comparison and ISSR profiling have also suggested it is closely related to Aloe forbesii, Aloe inermis, Aloe scobinifolia, Aloe sinkatana, and Aloe striata.[25] With the exception of the South African species A. striata, these Aloe species are native to Socotra (Yemen), Somalia, and Sudan.[25] The lack of obvious natural populations of the species has led some authors to suggest Aloe vera may be of hybrid origin.[26]

Distribution

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The natural range of A. 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.[12] This distribution is somewhat similar to the one of Euphorbia balsamifera, Pistacia atlantica, and a few others, suggesting that a dry sclerophyll forest once covered large areas, but has been dramatically reduced due to desertification in the Sahara, leaving these few patches isolated. Several closely related (or sometimes identical) species can be found on the two extreme sides of the Sahara: dragon trees (Dracaena) and Aeonium being two of the most representative examples.

The species was introduced to China and various parts of southern Europe in the 17th century.[27] The species is widely naturalised elsewhere, occurring in temperate and tropical regions of Australia, Barbados, Belize, Nigeria, Paraguay, Mexico and the US states of Florida, Arizona and Texas.[20][28] The actual species' distribution has been suggested to be the result of human cultivation.[21][29]

Cultivation

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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 for 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.[7] The species is hardy in zones 8–11, although it is intolerant of very heavy frost or snow.[8][30] 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.[31][32] In pots, the species requires well-drained, sandy potting soil and bright, sunny conditions; however, Aloe plants can burn under too much sun or shrivel when the pot does not drain the rain. The use of a good-quality commercial propagation mix or packaged "cacti and succulent mix" is recommended, as they allow good drainage.[33] Terra cotta pots are preferable as they are porous.[33] Potted plants should be allowed to completely dry prior to rewatering. When potted, aloes become crowded with "pups" growing from the sides of the "mother plant", they should be divided and repotted 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.[8] Large-scale agricultural production of Aloe vera is undertaken in Australia,[34] Bangladesh, Cuba,[35] the Dominican Republic, China, Mexico,[36] India,[37] Jamaica,[38] Kenya, Tanzania and South Africa,[39] along with the USA[40] to supply the cosmetics industry with Aloe vera gel.

This plant has gained the Royal Horticultural Society's Award of Garden Merit.[41]

 
Herbal farming in Chhattisgarh: Aloe vera
 
Aloe vera gel being used to make a dessert

Uses

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Scientific evidence for the cosmetic or therapeutic effectiveness of aloe vera is limited and frequently contradictory.[4][5] Despite this, the cosmetic and alternative medicine industries regularly make claims regarding the soothing, moisturizing, and healing properties of aloe vera[3][42] commercially advertised mainly for skin conditions such as sunburns, cold sores and frostbite. Aloe vera gel is also used commercially as an ingredient in yogurts, beverages, and some desserts,[43][44][45] although at certain doses, its toxic properties could be severe whether ingested or topically applied.[46] The same is true for aloe latex, which was taken orally for conditions ranging from glaucoma to multiple sclerosis until the FDA required manufacturers to discontinue its use.[47] Other uses for extracts of Aloe vera include the dilution of semen for the artificial fertilization of sheep,[48] as a fresh food preservative,[49] or for water conservation in small farms.[50] It has also been suggested that biofuels could be obtained from Aloe vera seeds.[51] Aloe is also used as a food substance, possibly for its gelling properties.

Traditional medicine

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Aloe vera is used in traditional medicine as a multipurpose skin treatment. In Ayurvedic medicine it is called kathalai, as are extracts from agave.[52]: 196 for aloe : 117 for agave  Early records of Aloe vera use appear in the Ebers Papyrus from the 16th century BC,[17]: 18  and in Dioscorides' De Materia Medica and Pliny the Elder's Natural History - both written in the mid-first century AD.[17]: 20  It is also written of in the Juliana Anicia Codex of 512 AD.[43]: 9  The plant is used widely in the traditional herbal medicine of many countries.[3]

Dietary supplement

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Aloin, a compound found in the exudate of some Aloe species, was the common ingredient in over-the-counter (OTC) laxative products in the United States until 2002 when the Food and Drug Administration banned it because the companies manufacturing it failed to provide the necessary safety data.[53][54] Aloe vera has potential toxicity, with side effects occurring at some dose levels both when ingested or applied topically.[46] Although toxicity may be less when aloin is removed by processing, Aloe vera that contains aloin in excess amounts may induce side effects.[3][6][55] A two-year National Toxicology Program (NTP) study on oral consumption of nondecolorized whole leaf extract of Aloe vera found evidence of carcinogenic activity in male and female rats. The NTP says more information is needed to determine the potential risks to humans.[56][57][58]

Aloe vera juice is marketed to support the health of the digestive system, but there is neither scientific evidence nor regulatory approval to support this claim.[59] The extracts and quantities typically used for such purposes appear to be dose-dependent for toxic effects.[46]

Commodities

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Aloe vera is used on facial tissues where it is promoted as a moisturiser and anti-irritant to reduce chafing of the nose. Cosmetic companies commonly add sap or other derivatives from Aloe vera to products such as makeup, tissues, moisturizers, soaps, sunscreens, incense, shaving cream, or shampoos.[43] A review of academic literature notes that its inclusion in many hygiene products is due to its "moisturizing emollient effect".[60]

Toxicity

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In 2011, the NTP carried out a series of short- and long-term carcinogenicity studies of a nondecolorized whole leaf extract of Aloe barbadensis miller (Aloe vera) in rats and mice, in which the extracts were fed to the rodents in drinking water.[3] The studies found "clear evidence of carcinogenic activity" in the rats, but "no evidence of carcinogenic activity" in the mice. Both the mice and rats had increased amounts of noncancerous lesions in various tissues. The NTP believes further studies of oral preparations of aloe are important, as are studies of the oral exposure of humans to aloe; topical preparations are still considered safe.[3]

Oral ingestion of Aloe vera may also cause diarrhea, which in turn can lead to electrolyte imbalance, kidney dysfunction, dry mouth, headache, and nausea, while topical application may induce contact dermatitis, erythema, or phototoxicity.[3][56]

Research into medical uses

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Two 2009 reviews of clinical studies determined that all were too small and faulty to allow strong conclusions to be drawn from them, but concluded, "there is some preliminary evidence to suggest that oral administration of aloe vera might be effective in reducing blood glucose in diabetic patients and in lowering blood lipid levels in hyperlipidaemia. The topical application of aloe vera does not seem to prevent radiation-induced skin damage. The evidence regarding wound healing is contradictory. More and better trial data are needed to define the clinical effectiveness of this popular herbal remedy more precisely."[6][61] One of the reviews found that Aloe has not been proven to offer protection for humans from sunburn, suntan, or other damage from the sun.[61]

A 2007 review of aloe vera's use in burns concluded, "cumulative evidence tends to support that aloe vera might be an effective interventions used in burn wound healing for first- to second-degree burns. Further, well-designed trials with sufficient details of the contents of aloe vera products should be carried out to determine the effectiveness of aloe vera."[62] Topical application of aloe vera may also be effective for genital herpes and psoriasis.[6][63] A 2014 Cochrane review found no strong evidence for the value of topical application of aloe vera to treat or prevent phlebitis caused by intravenous infusion.[64]

See also

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References

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  1. ^ Aloe vera (L.) Burm. f. Tropicos.org
  2. ^ Aloe vera (L.) Burm.f. is an accepted name . theplantlist.org
  3. ^ a b c d e f g h Template:Vcite2 journal
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  7. ^ a b c Yates A. (2002) Yates Garden Guide. Harper Collins Australia
  8. ^ a b c d Random House Australia Botanica's Pocket Gardening Encyclopedia for Australian Gardeners Random House Publishers, Australia
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  12. ^ a b "Aloe vera, African flowering plants database". Conservatoire et Jardin botaniques de la Ville de Genève. Retrieved 20 June 2008.
  13. ^ "Taxon: Aloe vera (L.) Burm. f." Germplasm Resources Information Network, United States Department of Agriculture. Retrieved 16 July 2008.
  14. ^ a b Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
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  17. ^ a b c Barcroft, A. and Myskja, A. (2003) Aloe Vera: Nature's Silent Healer. BAAM, USA. ISBN 0-9545071-0-X
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  21. ^ a b Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  22. ^ Linnaeus, C. (1753). Species plantarum, exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas. Vol. 2 pp. [i], 561–1200, [1–30, index], [i, err.]. Holmiae [Stockholm]: Impensis Laurentii Salvii.
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  26. ^ Jones WD, Sacamano C. (2000) Landscape Plants for Dry Regions: More Than 600 Species from Around the World. California Bill's Automotive Publishers. USA.
  27. ^ Farooqi, A. A. and Sreeramu, B. S. (2001) Cultivation of Medicinal and Aromatic Crops. Orient Longman, India. ISBN 8173712514. p. 25.
  28. ^ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  29. ^ "Aloe vera (Linnaeus) Burman f., Fl. Indica. 83. 1768." in Flora of North America Vol. 26, p. 411
  30. ^ "BBC Gardening, Aloe vera". British Broadcasting Corporation. Retrieved 11 July 2008.
  31. ^ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  32. ^ "Kemper Center for Home Gardening: Aloe vera". Missouri Botanic Gardens, USA. Retrieved 11 July 2008.
  33. ^ a b Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  34. ^ "Aloe vera producer signs $3m China deal". Australian Broadcasting Corporation. Retrieved 8 July 2008.
  35. ^ "More Medicinal Plants Grow in Ciego de Ávila". invasor.cu. Retrieved 25 June 2008. [dead link]
  36. ^ "Korea interested in Dominican 'aloe vera'". DominicanToday.com—The Dominican Republic News Source in English. Retrieved 19 July 2008.
  37. ^ Varma, Vaibhav (11 December 2005). "India experiments with farming medicinal plants". channelnewsasia.com.
  38. ^ "Harnessing the potential of our aloe". Jamaica Gleaner, jamaica-gleaner.com. Retrieved 19 July 2008.
  39. ^ "Kenya: Imported Gel Hurts Aloe Vera Market". allafrica.com. Retrieved 25 June 2008.
  40. ^ "US Farms, Inc. – A Different Kind of Natural Resource Company". resourceinvestor.com. Retrieved 19 July 2008.
  41. ^ "RHS Plant Selector Aloe vera AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 9 November 2012.
  42. ^ Kunkel. G. (1984) Plants for Human Consumption. Koeltz Scientific Books. ISBN 3-87429-216-9
  43. ^ a b c Reynolds, Tom (Ed.) (2004) Aloes: The genus Aloe (Medicinal and Aromatic Plants - Industrial Profiles. CRC Press. ISBN 978-0415306720
  44. ^ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  45. ^ "Yagua unveils cosmeceutical beverage". Decision News Media. Retrieved 20 June 2008.
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  47. ^ "Aloe". WebMD.
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  51. ^ Shukla, S. "Aloe Vera has biodiesel potential, reveals MSU study". The Indian Express. Retrieved 21 June 2008.
  52. ^ Quattrocchi, Umberto (2012) CRC World Dictionary of Medicinal and Poisonous Plants: Common Names, Scientific Names, Eponyms, Synonyms, and Etymology (5 Volume Set) CRC Press. ISBN 978-1420080445
  53. ^ "Aloe Vera : Science and Safety | NCCAM". Nccam.nih.gov. Retrieved 31 January 2014.
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  56. ^ a b "Aloe Vera – Side Effects and Cautions". National Center for Complementary and Alternative Medicine. Retrieved 7 October 2011.
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  58. ^ "NTP Speaks about Aloe Vera". Niehs.nih.gov. Retrieved 9 November 2012.
  59. ^ "Aloe (Aloe vera)". MayoClinic.com. 1 September 2012. Retrieved 9 November 2012.
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