Aloe vera 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
A. 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
is frequently contradicted by other studies.
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 their upper and lower stem surfaces. 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.
Like other
Aloe species,
Aloe vera forms
arbuscular mycorrhiza, a
symbiosis that allows the plant better access to mineral nutrients in soil.
Aloe vera leaves contain
phytochemicals under study for possible bioactivity, such as acetylated
mannans,
polymannans,
anthraquinone C-
glycosides,
anthrones,
anthraquinones, such as
emodin, and various
lectins.
Taxonomy and etymology
The species has a number of
synonyms:
A. barbadensis Mill.,
Aloe indica Royle,
Aloe perfoliata L. var.
vera and
A. vulgaris Lam.
Common names include Chinese Aloe, Indian Aloe, True Aloe, Barbados Aloe, Burn Aloe, First Aid Plant.
The species epithet
vera means "true" or "genuine".
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 and it has been suggested that the spotted form of
Aloe vera may be
conspecific with
A. massawana.
The species was first described by
Carl Linnaeus in 1753 as
Aloe perfoliata var.
vera,
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.
Techniques based on
DNA comparison suggest
Aloe vera is relatively closely related to
Aloe perryi, a species endemic to Yemen.
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.
With the exception of the South African species
A. striata, these
Aloe species are native to
Socotra (Yemen), Somalia, and Sudan.
The lack of obvious natural populations of the species has led some authors to suggest
Aloe vera may be of
hybrid origin.
Distribution
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.
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. 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.
The actual species' distribution has been suggested to be the result of human cultivation.
Cultivation
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.
The species is hardy in
zones 8–11, although it is intolerant of very heavy frost or snow.
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.
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.
Terra cotta pots are preferable as they are porous.
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.
Large-scale agricultural production of
Aloe vera is undertaken in Australia,
Bangladesh, Cuba,
the Dominican Republic, China, Mexico,
India, Jamaica,
Kenya, Tanzania and South Africa,
along with the USA
to supply the cosmetics industry with
Aloe vera gel. This plant has gained the
Royal Horticultural Society's
Award of Garden Merit.
Uses
6000 year old stone carvings in Egypt contain images of the plant,
which they referred to as the "plant of immortality". It was given as a
burial gift to deceased pharaohs.
Preparations made from
Aloe vera are often referred to as "aloe vera".
Scientific evidence for the cosmetic and therapeutic effectiveness of
aloe vera is limited and when present is frequently contradictory.
Despite this, the cosmetic and alternative medicine industries
regularly make claims regarding the soothing, moisturizing, and healing
properties of aloe vera
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;
although at certain doses, its toxic properties could be severe whether ingested or topically applied.
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. Other uses for extracts of
Aloe vera include the dilution of
semen for the artificial fertilization of sheep,
as a fresh food preservative,
or for
water conservation in small farms.
It has also been suggested that biofuels could be obtained from
Aloe vera seeds.
Aloe is also used as a food substance, possibly for its gelling properties.
Traditional medicine
Aloe vera is used in traditional medicine as a multipurpose skin treatment. In
Ayurvedic medicine it is called
kathalai, as are extracts from
agave.
Early records of
Aloe vera use appear in the
Ebers Papyrus from the 16th century BC
, and in
Dioscorides' De Materia Medica and
Pliny the Elder's Natural History - both written in the mid-first century AD.
It is also written of in the
Juliana Anicia Codex of 512 AD.
The plant is used widely in the traditional herbal medicine of many countries.
Dietary supplement
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.
Aloe vera has potential toxicity, with
side effects occurring at some dose levels both when ingested or applied topically.
Although toxicity may be less when aloin is removed by processing,
Aloe vera that contains aloin in excess amounts may induce side effects.
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.
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.
The extracts and quantities typically used for such purposes appear to be dose-dependent for toxic effects.
Commodities
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.
A review of academic literature notes that its inclusion in many
hygiene products is due to its "moisturizing emollient effect".
Toxicity
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.
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.
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.
Research into medical uses
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. It might be useful as a treatment
for genital herpes and psoriasis. 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."
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.
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."
Topical application of aloe vera may also be effective for
genital herpes and
psoriasis.
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.
—From Wikipedia