Common Name: Aloe Vera

General Information

Aloe vera is a succulent, evergreen perennial herb that can be stemless or with a short stem up to 30cm long; it can produce a flowering stem up to 160cm tall[, ]. Freely suckering, it produces dense rosettes of 16 - 20 long pointed leaves from shortly branched creeping rhizomes[, ].
The plant is a very popular herbal medicine that has a history of use dating back to at least 400 BC. It is widely cultivated, from warm temperate to tropical regions, as a medicinal plant and ingredient of skin care products. It is also commonly grown as an ornamental in gardens and as a pot plant in regions where it is not warm enough to grow it outdoors.

Known Hazards

Aloe vera is very widely used as a herbal remedy. Whilst the leaf gel is entirely safe, the bitter aloes found at the base of the leaves contain anthraquinones which have potential problems if used in excess. The possible side effects of anthraquinones include congestion and irritation of the pelvic organs[]. Anthraquinone laxatives may also play a role in development of colorectal cancer as they have genotoxic potential, and tumorigenic potential[].

Botanical References

,

Range

Only known as a cultivated or naturalized plant., it is generally presumed to have originated in Arabia, Somalia or Sudan.

Habitat

Maritime sands and rocks[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Perennial
Height	0.80 m
Growth Rate	Slow
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Aloe vera can be grown outdoors from the warm temperate zone to the tropics. It grows best in areas where annual daytime temperatures are within the range 19 - 27°c, but can tolerate 10 - 35°c[]. It can tolerate occasional, light, short-lived frosts, experincing only slight damage at -3°c so long as conditions are fairly dry[, ]. It prefers a mean annual rainfall in the range 1,900 - 3,000mm, but tolerates 700 - 4,000mm[]. During the winter months in the subtropics, the plant becomes dormant and utilizes very little moisture[].
Prefers a sunny position, but can tolerate light shade[]. Requires a well-drained soil, preferring one that is sandy or loamy[]. Prefers a rich soil, but is tolerant of poor soils[, ]. Tolerates some salinity in the soil[]. Prefers a pH in the range 6.5 - 7.5, tolerating 6 - 8[]. Established plants will survive drought quite well even though the root system is relatively shallow[].
Aloe vera plants take about 3 years to attain harvestable size, and then leaves can be harvested for about seven years. The exudate is collected by cutting off the leaves transversely close to the stem and positioning them in such a way that the juice drains into pots, tubs, vessels or even a simple canvas placed over a depression in the ground. The exudate may also be obtained by squeezing the leaves or by warm or cold water retting. The leaves are usually cut in the morning and it takes 4 - 5 hours for the juice to drain from a pile of leaves. Only older leaves are cut; younger ones and growing tips are spared[].
For gel production, the leaves are cut at intervals of about 3 months. The youngest leaves, less than 25cm long, are not suitable because of their low gel content, but the leaves should not be too old because gel quantity and quality may decline[].
In Africa, Aloe vera flowers and produces fruits normally, but elsewhere fruit formation is rare. Failure to set fruit is presumed to be caused by pollen sterility and self-incompatibility. Birds are the most important pollinators of Aloe species, but in Africa honeybees also play a role[].
Aloe species follow the Crassulacean acid metabolism (CAM). CAM plants can fix carbon dioxide at night and photosynthesize with closed stomata during the day, thus minimizing water loss. This, plus their succulent leaves and stems, and the presence of a thick cuticle, makes them well adapted to dry conditions[].

Edible Uses

Leaves - cooked[]. Very bitter, they are an emergency food that is only used when all else fails[].
A gel in the leaves is sometimes used as an ingredient of commercial jellies, drinks and ice cream[, ]. As a food supplement, the leaf gel is said to facilitate digestion, and to improve blood and lymphatic circulation, as well as kidney, liver and gall bladder functions[].

Seed[, ]. An emergency food used when all else fails[].

The exudate from the base of the leaves is used as a bittering agent for food and beer[].

Medicinal

Aloe vera is a well known herbal preparation with a long history of use. It is widely used in modern herbal practice and is often available in proprietary herbal preparations[]. All parts of the plant can be used, but the two most common parts being the clear gel contained within the leaves and the bitter exudate at the base of the leaf.

Aloe vera gel has earned a reputation as a miracle drug. It is effective in burn treatment, because of its anti-inflammatory and wound-healing properties. Its healing properties may be due to rehydrating, insulating and protective activities resulting from the high water content. The major constituents are polysaccharides (mainly acemannan), lectins, sterols and enzymes, and the effect is assumed to be a synergy between the polysaccharide base and various components. In addition, acemannan has shown immune stimulating, anticancer and antiviral effects[].
Several studies on both topical and oral treatments with the gel have shown a positive influence on the synthesis of glycosamino glycans, thereby facilitating wound healing.
A placebo-controlled, double-blind study showed that a topically applied gel of 0.5% in a hydrophylic cream is beneficial for patients suffering from psoriasis. It did not show toxic or other side-effects.
A clinical test with patients with advanced solid tumours, for whom no standard effective therapy was available, suggested that the gel, in combination with the immunomodulating neurohormone melatonin, may produce some therapeutic benefits, at least in terms of stabilization of disease and survival.
The dried exudate of bitter aloes contains 15 - 40% anthraquinone derivatives such as aloin and hydroxyaloins. Furthermore, the exudate contains the pyrone derivative aloenin and aloeresins[].
The compound responsible for the laxative properties is aloin, which itself is inactive as a laxative, but is activated to aloe-emodin anthrone in the body by the action of Eubacterium species[].
It has been claimed that aloin is responsible for antihistamine and anti-inflammatory activity[].
Both aloin and aloeresin B have skin-whitening activity[].
Large variations in aloin content have been found in Aloe vera, with the highest concentration in exudates from younger mature leaves[].
Contradicting results of clinical tests with Aloe vera products are common. A problem is that the identity of the tested plants is not always certain. A second problem is that the products are not of standard composition, but depend on cultivar, growing conditions and handling after harvest. Therefore, commercial products may vary enormously in composition. Also, contamination of the gel with exudate can turn a harmless product into a purgative. It is therefore imperative that products of well-defined composition are used for clinical trials, that the identity of the plant is confirmed by a taxonomist and that a specimen is deposited in a herbarium for future reference[].

The clear gel contained within the leaf makes an excellent treatment for wounds, burns and a host of other skin disorders, placing a protective coat over the affected area, speeding up the rate of healing and reducing the risk of infection. The gel is also applied externally to cure haemorrhoids[, , ]. These actions are in part due to the presence of aloectin B, which stimulates the immune system[]. To obtain this gel, the leaves can be cut in half along their length and the inner pulp rubbed over the affected area of skin[]. This has an immediate soothing effect on all sorts of burns and other skin problems[].
The use of the gel has been approved in the United States for the treatment of leukaemia in cats, of fibrosarcoma in dogs, for wound healing in humans and to prevent dry socket (‘alveolar osteitis’) in humans[].
The peeled leaves are eaten to relieve sore throat and coughs and as a mild laxative. As a food supplement, the leaf gel is said to facilitate digestion, and to improve blood and lymphatic circulation, as well as kidney, liver and gall bladder functions[]. There are claims of beneficial activity of Aloe vera products in cases of AIDS, arthritis, or other chronic and debilitating conditions. However, these claims have not been substantiated by scientific studies. There is also no evidence that topical Aloe vera gel is effective in preventing or minimizing radiation-induced skin reactions in cancer patients. In large amounts, the gel has anti-irritant properties[].

A bitter substance is obtained from the yellow sap at the base of the leaf. Known as ‘bitter aloes’, it contains anthraquinones which are a useful digestive stimulant and a strong laxative[]. It also has vermicidal properties[]. It is taken internally in the treatment of chronic constipation, poor appetite, digestive problems etc[]. Mixed with other ingredients to mask its bitter taste, it is taken against asthma and to treat coughs. Similar mixtures are taken to cure dysentery, kidney problems or against dyspepsia[]. It should be administered preferably in combination with an antispasmodic to moderate its griping action[].
It is applied externally as a refrigerant to treat acne or cuts[].
'Curaçao aloe' should contain at least 28% hydroxy-anthraquinone derivatives; it is almost entirely soluble in 60% alcohol and for more than 70% in water. It should not contain more than 12% moisture and 3% ash[].
The plant is strongly purgative so great care should be taken over the dosage[].
Anthraquinone-based laxatives, such as bitter aloes, should not be used longer than 8 - 10 days, nor by children younger than 12 years. Contra-indications include pregnancy, breastfeeding, intestinal inflammations and haemorrhoids[, , ].
When plants are grown in pots the anthraquinone content is greatly reduced[].

The plant is emmenagogue, emollient, laxative, purgative, stimulant, stomachic, tonic, vermifuge and vulnerary[, , , , , , ]. Extracts of the plant have antibacterial activity[].

The plant is used to test if there is blood in the faeces[].

This plant has a folk history of treatment in cases of cancer[].

Other Uses

The leaf extracts are used in skin-care cosmetic products[, ].

The gel obtained from the leaves is used in a coating on grapes to lengthen the shelf life considerably. This patented method could also be applicable in other high-value fruits and vegetables[].
A novel application of gel powder is as a 1% addition to concrete, which gives the reinforcing steel better resistance against corrosion[].

Plants have been grown indoors in pots in order to help remove toxins from the atmosphere. It is also unusual in that it continues to release oxygen and absorb carbon dioxide in the dark, making it very suitable for growing in bedrooms[].

Propagation

Seed - sow in seed trays in a lightly shaded position - the seed usually germinates in 1 - 6 months at 16°c. Prick out the seedlings into individual pots of very well-drained soil when they are large enough to handle and grow them on until large enough to plant out.
Division of offsets when available,. The plants produce offsets quite freely and they can be divided at any time of the year as long as it is warm enough to encourage fresh root growth to allow re-establishment of the plants[]. They can be cut from the mother plant when they are 15 - 20cm long. They may be grown in a nursery during the first year[].

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