Aloe Vera

Aloe vera is an ancient herbal remedy that may be able to accelerate wound healing and treat ailments such as dermatitis and psoriasis. It is also a moisturizer that can potentially lighten the skin and prevent wrinkle formation.

Effects


Grade Level of Evidence
A Multiple double-blind, controlled clinical trials.
B 1 double-blind, controlled clinical trial.
C At least 1 controlled or comparative clinical trial.
D Uncontrolled, observational, animal or in-vitro studies only.
Grade Effect Size of Effect Comments

A

Psoriasis treatment

Strong

Clears psoriatic plaques efficiently, and is more effective than the corticosteroid triamcinolone acetonide.

C

Skin lightening

Strong

Induces skin lightening by suppressing melanin formation and by causing the aggregation of melanin within melanophores.

C

Increased skin hydration

Moderate

Appears to act as a humectant, drawing water to the stratum corneum.

C

Healing

Moderate

Speeds up the healing of wounds, burns, skin ulcers and anal fissures by promoting re-epithelialization and angiogenesis, as well as through its anti-inflammatory and antimicrobial properties.

C

Dermatitis treatment

Mild

Can improve diaper dermatitis and possibly also atopic dermatitis and irritant contact dermatitis.

D

Wrinkle treatment

Mild

Topical and dietary aloe vera may protect against the formation of wrinkles by increasing the production of type 1 collagen and inhibiting its breakdown.

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Scientific Research


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Table of contents:

1. Sources

Aloe vera or Aloe barbadenis Miller is a succulent plant that is widely distributed in Asia, Africa, Europe and America.[1][2] Its healing properties has been recognized by various cultures for millenia;[1][3] among the earliest recorded medicinal uses can be found on a Sumerian tablet that dates back to 2100 BC, and the Papyrus ebers, an Egyptian document that dates back to 1550 BC, states that aloe vera's medicinal values had been acclaimed for many centuries prior.[4] Modern clinical use of aloe vera began in the 1930s, when the gel from the leaf pulp of the plant was reported to successfully treat X-ray and radium burns to the skin and mucous membranes.[5]

Aloe vera leaves contain a large number of biologically active substances that account for its therapeutic effects, such as vitamins, enzymes, minerals, sugars, lipids and phenolic compounds.[1][6][7]

Apart from its medical uses, aloe vera is also utilized as a source of functional foods, in milk, ice cream and confectionery, and sometimes as a flavouring component and preservative.[6] It is also a valuable ingredient in the cosmetic and toiletry industry where it has been used as a base material for the production of creams, lotions, soaps, shampoos and other products.[7][8] An analysis of 52 moisturizers for acne revealed that 9 (17%) contained aloe vera as an anti-inflammatory agent,[9] and an investigation of 400 dermatology outpatients reported that 16% of the herbal medicinal or cosmetic products the patients used contained aloe vera.[10]

2. Bioavailability

2.1 Oral administration

Although we were not able to find any studies on the oral bioavailability of aloe vera, aloe vera preparations have been shown to increase the bioavailability of several vitamins including vitamin C, vitamin E and vitamin B12 in humans, possibly by protecting against their degradation in the intestinal tract.[11][12]

Aloe vera also has the potential to enhance the intestinal absorption of drugs. It reduced the transepithelial electrical resistance (TEER) of human intestinal epithelial cell monolayers and rat intestinal tissue, indicating the opening of the tight junctions between adjacent epithelial cells.[13][14] In another study, aloe vera gel did not inhibit the efflux of cimetidine across excised rat intestinal tissue, but polysaccharides precipitated from the gel did show an inhibitory effect, suggesting another mechanism of action.[15]

2.2 Topical administration

An in vitro experiment using porcine ear skin showed that some components of aloe vera permeate the skin readily, but these components were not identified.[16] In addition, the same study found that aloe vera juice enhanced the penetration of colchicine, oxybutynin and quinine into porcine ear skin, but not for caffeine or mefenamic acid.[16] Pre-treatment of porcine skin with aloe vera juice also did not enhance the in vitro permeation of ketoprofen.[17] Because the permeation enhancement ratio seems to increase with molecular weight, it has been proposed that larger molecules are better able to displace components of aloe vera from permeation pathways across the skin, allowing increased scope for the molecule to interact with the enhancing factor in aloe vera and complex with it before being transported across the skin.[16]

A gel formulation containing Sepigel 305 has been proven to reduce the release and permeation of aloin, an anthraquinone in aloe vera, which is beneficial as human skin fibroblasts can metabolize absorbed aloin into a structurally related compound that increases the sensitivity of skin to ultraviolet light.[18]

3. Effects on the skin

3.1 Antioxidant action

Aloe vera extracts are good natural sources of antioxidants.[19][20] A peroxidase has been identified in a commercial gel of aloe vera,[21] and a chromone with potent superoxide anion scavenging activity has also been found.[22] More generally, there is a correlation between the phenolic content of aloe vera extracts and their antioxidant capacity.[23]

However, one study showed that an aloe vera extract did not affect the total antioxidant capacity of a human skin EpiDerm model.[24] More importantly, studies have also indicated that the exposure of aloe vera extracts to UVA light may lead to the generation of free radicals that cause oxidative damage.[25][26][27]

3.2 Photoprotection

Lyophilized crude and methanolic extracts of aloe vera gel can partly block UVB radiation.[28] Although an early study found that aloe vera did not affect cutaneous erythema following UVB exposure,[29] a more recent investigation has shown otherwise, with an aloe vera gel significantly reducing UV-induced erythema on the backs of human volunteers in a double-blind, placebo-controlled trial.[30] Aloe vera gel extracts were also able to prevent UVB-induced immunosuppression in murine skin and epidermal cells by reducing keratinocyte-derived immunosuppressive cytokines and by restoring the accessory cell function of epidermal Langerhans cells.[31][32][33][34]

In addition, the compound aloin has demonstrated protective effects against UVA-induced oxidative injury, decreased collagen synthesis and inhibition of proliferation in cultures of dermal fibroblasts.[35] It is important to also take into consideration, however, the evidence that aloe emodin, a metabolite of aloin A, may cause phototoxicity.[25][26][27]

3.3 Anti-inflammatory effect

Aloe vera has shown its anti-inflammatory activity in a number of experimental models, including rat paw edema and ear swelling.[36][37][38] In one study, a chromone compound isolated from aloe vera exhibited topical anti-inflammatory activity equivalent to 200 microg/ear of hydrocortisone.[39] Aloe-emodin and aloin, 2 anthraquinones derived from aloe vera, may also be key constituents responsible for its anti-inflammatory activity, as there is evidence that they suppress inflammatory responses by blocking inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) mRNA expression.[40]

3.4 Increased moisturization

In a randomized vehicle-controlled study on 20 women, cosmetic formulations supplemented with 0.1%, 0.25% and 0.5% freeze-dried aloe vera extract increased the water content of the stratum corneum significantly compared to the vehicle, after twice-daily applications for 1 or 2 weeks. The 3 formulations did not differ after a 1-week period of application, but after a 2-week period, the formulation containing the greatest concentration of aloe vera extract produced the highest skin hydration values. Transepidermal water loss did not change, indicating that the extract did not act by an occlusive mechanism. Rather, it has been hypothesized that the monosaccharides and polysaccharides present in the aloe vera extracts are hygroscopic and act as humectants, while the amino acids they contain improve water retention in the stratum corneum.[41] Acemannan, the major polysaccharide of aloe vera gel, also appears to be an excellent emollient with moisturizing capability.[42]

When 6 marketed herbal moisturizers in India were compared, the formulation containing wheat germ oil, olive oil and aloe vera extract produced the highest skin hydration effect on the forearm skin of human volunteers, followed by the formulation containing aloe vera extract and olive oil.[43] A prophylactic moisturizing cream containing metal esculetina, gingko biloba and aloe vera showed good results in improving skin hydration and preventing radiation-induced dermatitis in a small group of breast cancer patients undergoing radiotherapy.[44]

Another study compared the moisturizing effects of pure aloe gel materials dissolved in water to obtain 3% solutions. Aloe vera gel was more hydrating to forearm skin after a single application than aloe ferox gel (which had a dehydrating effect), but was slightly less hydrating than aloe marlothii gel. Nevertheless, one of the changes were statistically significant compared to the placebo, deionized water. A longer-term trial however found that all 3 aloe gel materials dehydrated instead of hydrating the skin over a 4-week treatment period, especially aloe marlothii.[45]

3.5 Lightening effect

Aloe vera contains at least 3 compounds that can potentially lighten the skin. Aloesin, a chromone, has been proven to inhibit tyrosinase from mushroom, human and murine sources. It is both a competitive and noncompetitive inhibitor.[46][47][48] Aloesin also suppressed melanogenesis and pigmentation in pigmented skin equivalents, though more weakly than tea polyphenols.[49][50] Moreover, aloesin topically applied on human forearm skin 4 times a day for 15 days dose-dependently inhibited UV-induced hyperpigmentation in a vehicle-controlled study.[51]

Different experiments disagree on whether aloesin's depigmenting effect is stronger or weaker than arbutin's.[49][51] What is clear, however, is that aloesin and arbutin act synergistically to reduce tyrosinase activity and melanin content.[51][52][53]

Aloin and 2-O-feruloylaloesin are also tyrosinase inhibitors. Aloin is a mixed-type inhibitor, whereas 2-O-feruloylaloesin has been shown to inhibit mushroom tyrosinase noncompetitively.[46][54] There is also evidence that suggests that aloin causes melanin aggregation in melanophores. This leads to skin lightening because when melanin is not dispersed, pigments in other chromatophores are exposed to light and the skin takes on their hue.[55][56]

Aloe vera leaf gel and aloin inhibit collagen breakdown by matrix metalloproteinases (MMPs),[57] and aloe vera gel and aloesin increase type I collagen synthesis.[58][59] Interestingly, liposome-encapsulated aloe vera gel significantly enhanced the increased in type I collagen production (23% versus 4% for unencapsulated aloe vera gel) in human fibroblasts, possibly because the liposomes enable greater penetration into the cells.[58] Further, extracts from immature shoots of aloe vera (1-month-old), which contain higher contents of aloesin and aloins, are more effective than extracts from adult shoots (4-months-old), since human dermal fibroblasts treated with the former after UVB irradiation suppressed MMP-1 and MMP-3 levels and elevated type I procollagen production to a greater extent than the latter.[59] Since a decrease in type I collagen induces wrinkle formation,[60] this suggests that aloe vera protects against skin wrinkling.

Dietary aloe vera also has anti-aging properties. When 30 women aged 45 and above took either 1,200 mg or 3,600 mg of aloe vera gel supplementation daily for 90 days, facial wrinkles as measured by a skin replica and a Visiometer diminished in both groups, while cutometer measurements indicated that skin elasticity increased significantly in the lower-dose group. Biopsies from 6 individuals revealed that the levels of MMP-1 mRNA in buttock skin were significantly lower compared to baseline after aloe vera intake, consistent with the decreased wrinkling. Type I procollagen mRNA levels were also increased in both groups, but not to a significant extent.[61]

In another study, herbal cosmetic creams containing ethanolic extracts of licorice, turmeric roots, babchi seeds, the legume Cassia tora, areca palm, pomegranate, amla fruits, gotu kola leaves, the dried bark of Ceylon cinnamon and the fresh gel of aloe vera in various concentrations (0.12% to 0.9%) were formulated and tested for their effects on skin hydration and viscoelastic properties. The cream base was prepared with almond oil, sesame, honey, cetyl alcohol, stearic acid, polysorbate monoleate, sorbitan monostearate, propylene glycol and glycerin. 18 men and women applied the creams to the back of their volar forearms. After 6 weeks, 2 of the formulations led to increases in extensibility by 32% and 30%, firmness by 29% and 30%, and skin hydration by 16% and 18%, respectively.[62]

3.7 Anti-microbial activity

Aloe vera extracts inhibit many bacterial species, including Klebsiella, Enterobacter, Pseudomonas, Staphylococcus, Micrococcus and E. coli, even those strains that are multidrug resistant, such as MRSA.[63][64]

Anthraquinone compounds such as aloin and aloe emodin appear to be the active antibacterial components. The glycoside in particular makes it easy for aloin to invade cells, enhancing its activity.[65]

However, a cosmetic emulsion with 2.5% aloe vera extract failed to inhibit microbial growth in vivo, indicating that aloe vera may not be suitable for use as a natural preservative.[66]

3.8 Acne treatment

In a randomized, double-blind, prospective 8-week trial, the combination of 0.05% tretinoin cream and 50% aloe vera gel showed superior efficacy in reducing non-inflammatory and inflammatory lesions in patients with mild-to-moderate acne vulgaris, compared to treatment with the tretinoin cream alone. The combination therapy was also better-tolerated, causing significantly less severe erythema.[67]

3.9 Psoriasis treatment

Aloe vera leaf gel showed an anti-psoriatic activity of 82% in a mouse tail model of psoriasis, nearly equivalent to the effect of tazarotene (88%).[68]

The anti-psoriatic effect of aloe vera has been validated in double-blind and placebo-controlled clinical trials. The first trial enrolled 60 patients, half of which were given 0.5% aloe vera extract in a hydrophilic cream and the other half a placebo. By the end of the treatment, the aloe vera cream had significantly cleared psoriatic plaques in 83% of the patients, compared to 8% in the placebo group.[69] The second study found that a commercial aloe vera gel was not better than placebo, but this was probably due to the use of an inappropriate placebo, given that the placebo had a high response rate in its own right.[70] A third trial compared the efficacies of a topical aloe vera cream and a cream with 0.1% triamcinolone acetonide. The aloe vera cream reduced the symptoms of mild-to-moderate psoriasis more effectively, confirming the results of the first study that indicated that aloe vera is a viable treatment option.[71]

3.10 Dermatitis treatment

Aloe vera gel modulates immunological responses in atopic dermatitis in mice through influencing the level s of the inflammatory cytokines IL-5 and IL-10.[72]

In a comparative trial, infants receiving treatment with aloe vera cream 3 times a day for 10 days experienced improvement in the severity of diaper dermatitis, though those treated with a marigold ointment had significantly fewer rash sites.[73]

Gloves impregnated with aloe vera have been used for the management of dry skin and irritant contact dermatitis caused by occupational exposure.[74]

3.11 Improved healing

In vitro and animal studies indicate topical aloe vera as a potential treatment for acute and chronic wounds. Several components of aloe vera have been proposed to account for its healing properties. Mannose-6-phosphate, the main sugar in aloe vera gel, is known to possess anti-inflammatory activity and both it and the mucopolysaccharide acemannan are thought to stimulate the proliferation of fibroblasts, which ultimately helps promote collagen deposition and re-organization.[75][76] Indeed, a recent study confirmed that mannose-rich aloe vera polysaccharides positively regulated the production of extracellular matrix components, enhancing the expressions of collagen, n-acetyl glucosamine, n-acetyl galactosamine and that of the metalloproteinase inhibitor TIMP-2 compared to untreated wounds.[77] A glycoprotein fraction isolated from aloe vera gel too exhibited wound healing activity by promoting cell proliferation and migration.[78]

When applied to dermal wounds in rats, aloe vera increased the synthesis of glycosaminoglycans (GAGs), which form the ground substance that is laid down in the early stage of wound healing.[79] It also increased the synthesis and cross-linking of collagen in the granulation tissue, which contributes to wound strength.[80][81][82] Aloe vera gel also accelerated the re-epithelialization and angiogenesis of surgical incisions more compared to 1% silver sulfadiazine and a topical thyroid hormone cream.[83][84]

Aloe vera gel also expedited cutaneous healing compared to untreated controls or saline controls.[85][86][87][88][89] Because an aqueous cream placebo healed full-thickness excision wounds in rats significantly quicker than saline, it may be that the high water content in aloe vera also helps in the healing process.[90]

Aloe vera also appears to possess therapeutic efficacy in treating burns due to its anti-inflammatory, antimicrobial and wound healing properties.[91][92] Relative to controls, both fresh aloe vera gel and a stable aloe vera cream enhanced the healing of first-, second- and third-degree burns in mice.[93] Similarly, aloe vera gel improved cutaneous microcirulation and wound healing of second-degree burns in rats to a greater extent than saline treatment,[94] and aloe vera gel dressings healed full-thickness burns on guinea pigs 20 days sooner than plain gauze occlusive dressings.[95] Only one study found that compared to no treatment, aloe vera did not improve re-epithelialisation, scar strength, scar depth or the cosmetic appearance of the scar when applied to a porcine deep dermal contact burn.[96]

There is no agreement on whether aloe vera is more effective in treating burn wounds than 1% silver sulfadiazine; one study found that an aloe vera cream increased re-epithelialization and decreased the wound size significantly compared to 1% silver sulfadiazine cream,[97] and another showed that aloe vera gel suppressed inflammation of deep-partial thickness burn wounds more so than 1% silver sulfadiazine,[98] but a third study using an aloe vera gel showed otherwise.[99]

Aloe vera's anti-inflammatory effect may also explain its healing of skin ulcers.[100] Topical application of aloe vera gel to diabetic rats for 9 days significantly increased the levels of glycosaminoglycans, improving the healing of the ulcer and its breaking strength relative to untreated controls.[101]

Several clinical trials investigating the healing effects of aloe vera have been performed on human patients. 4 trials recruited patients with burns. Of these, one found that aloe vera cream led to faster healing of the burns in 18 days compared to 30 days for framycetin cream, but the standard deviations were not reported, making it impossible to confirm the validity of the result.[102] 2 studies noted that the number of days taken for healing of partial thickness burns was lower when treated with aloe vera than topical silver sulfadiazine or petrolatum gauze, but the outcome measure (mean time to wound healing) is inappropriate because it requires the exclusion of patients who did not heal, therefore introducing bias.[103][104] The last study found that topical aloe vera cured 55% of minor burns compared to silver sulfadiazine which had a cure rate of 39%, but the difference was not statistically significant.[105]

1 trial evaluated the effects of aloe vera cream in reducing postoperative pain, postdefection pain, and promoting wound healing after open hemorrhoidectomy. 49 patients were randomly allocated to either a 0.5% aloe vera cream or a placebo cream deemed to have no healing properties. Subjects in the aloe vera cream group not only had significantly less postoperative and postdefection pain, all of their wounds were completely healed at 14 days compared to only 1 out of 24 patients (4%) in the placebo group. This difference was statistically significant.[106]

1 trial assessed the effects of another topical cream containing 0.5% aloe vera juice powder in the treatment of chronic anal fissures. The cream was applied 3 times a day for 6 weeks, and there were statistically significant differences in pain, hemorrhaging upon defection and wound healing after only the first week of treatment, compared to the control group.[107]

1 trial recruited patients who had recently undergone a shave biopsy excision for suspected skin cancer. Participants were allocated to receive either an Aloe vera derivative gel dressing (Carrasyn hydrogel) or conventional therapy consisting of initial cleansing of the wound with hydrogen peroxide followed by the application of antibiotic ointment and an adhesive dressing. All patients in both groups were completely healed after 2 weeks.[108]

1 trial found that Carrasyn hydrogel dressing was not superior to a moist saline gauze wound dressing in healing pressure ulcers, and another stated that wounds resulting from caesaran section or laparotomy for gynecologic surgery healed more quickly when treated with aloe vera gel than when treated with a standard wound treatment protocol involving a wet-to-dry dressing that was applied using a solution equal parts saline and 0.025% sodium hypochlorite. Yet another trial compared the treatment of faces that had undergone full-face dermabrasion using standard polyethylene oxide gel wound dressings on one side, and polyethylene oxide gel dressings saturated with stabilized aloe vera on the other. Wound healing was approximately 72 hours faster on the side treated with aloe vera. However, all three studies used time to complete wound healing as an outcome measure, which is not appropriate and increases the risk of bias.[109][110][111][112]

As many of these human studies suffered from methodological flaws, a systematic review conducted in 2012 concluded that there is still an absence of high quality clinical trial evidence to support the use of topical aloe vera or aloe vera dressings as treatments for acute and chronic wounds.[113]

3.12 Protection against radiotherapy-induced skin reactions

Interest in the use of aloe vera to treat radiation burns was aroused in the 1930s by the paper of Collins and Collins,[114] who tried it because it was used for severe sunburn in Florida.[115] Many other case reports of treatment soon followed.[116][117][118]

Because the literature in the 1930s consisted primarily of reports of case histories, in 1940 and 1941 Rowe investigated the effects of aloe vera gel on radiation burns in rats under laboratory conditions. The first experiment was not conclusive, whereas the second found that rats treated with the aloe vera gel showed an increased rate of healing over the control rats.[119][120]

With the development of atomic energy, the US goverment began to take an interest in the possible applications of aloe vera in military and civilian radiation medicine. In 1953, two researchers working for the US Atomic Energy Commission showed that lesions induced in rabbits by exposure to beta radiation were completely healed in 2 months using fresh aloe vera and an aloe vera ointment, whereas untreated areas were not completely healed even at the end of 4 months.[121] However, researchers working for the US Army published extensive clinical and laboratory studies on aloe vera 4 years later which suggested that the plant did not have any useful curative properties. In one experiment, 18 rats and 22 rabbits were exposed to gamma radiation to create uniform ulcers, before being treated with aloe vera ointment, fresh leaf or left untreated. The animals treated with aloe vera took the same time or longer to heal than the controls, indicating no beneficial effect of the treatment.[122]

Several clinical trials have been conducted on the effects on aloe vera on patients receiving radiotherapy treatment. In a non-blinded three-armed study, an aloe vera lotion was not superior to no lotion in reducing radiotherapy-induced erythema in breast cancer patients.[123] This did not agree with the results of another unblinded, self-controlled trial, which found that an aloe vera lotion decreased the intensity of radiation-induced dermatitis.[124]

Another trial, which was blinded, found that aloe vera gel seemed to have a protective effect against skin reactions when added to mild soap at high cumulative dose levels, compared to use of the mild soap alone.[125] A third trial tested commercial moisturizing creams and concluded that all of the topical products, including one that contained aloe vera (Radioskin 2), helped lower the incidence of skin side effects in patients treated with radiotherapy for breast cancer.[44]

However, 3 phase III trials showed that aloe vera gel was not an effective prophylactic agent for radiation-induced skin toxicity,[126][127] and another found that an anionic phospholipid-based cream was better than an aloe vera-based gel in preventing radiation dermatitis in pediatric patients.[128]

If aloe vera does indeed protect against radiotherapy-induced skin reactions, it may exert its radioprotective effects by preventing radiation-induced biochemical alterations such as the decrease in antioxidant levels and the increase in lipid peroxidation, as has been demonstrated in mice,[129] and by inhibiting the apoptosis of irradiated cells.[130]

3.13 Chemoprevention

In the absence of UV radiation, aloe vera has anti-tumour effects; it protected against dimethylbenz(a)anthracene- and croton oil-induced skin papillomagenesis in mice.[131][132] The anthraquinone aloe emodin is more cytotoxic to cancer cells than noncancerous skin cells, indicating that it may be useful as an anti-cancer agent, especially in liposomal formulations.[133][134][135] Another anthracycline, aloin, appears to possess antineoplastic and antimetastatic properties as it suppressed the cell proliferation, adhesion and invasion abilities of murine melanoma cells.[136]

3.14 Other effects and uses

Aloe vera may be useful for treating skin injuries caused by sulfur mustard exposure[137][138][139] or extravasation,[140] and for treating scabies,[141] but there is no strong evidence for its prevention and treatment of infusion phlebitis.[142]

4. Safety

In its 2007 report, the Cosmetic Ingredient Review Expert Panel concluded that aloe vera flower extract, leaf extract, leaf juice, polysaccharides and leaf water are safe as cosmetic ingredients if their anthraquinone levels do not exceed 50 ppm.[143]

4.1 Adverse skin reactions

Herbal remedies and cosmetics should be regarded as a potential source of adverse skin events despite the common belief that botanical extracts are innocuous.[10]

There are some few case reports of allergic sensitization and contact dermatitis to aloe vera in the literature.[144][145][146][147] It has been recommended that elderly individuals who suffer from dry skin should take care to avoid aloe vera in emollients because it has the potential to be a skin sensitizer.[148]

Nevertheless, allergic reactions to aloe vera are considered rare. In one study, out of 702 consecutive patients patch tested with an oily extract from the leaves, Aloe pulvis from the entire plant and concentrated Aloe vera gel, none showed any reaction to any of the preparations.[149]

4.2 Cytotoxicity

When 4 commercial preparations of stabilized aloe vera gel samples were tested on human endothelial cells and fibroblasts, 2 were cytotoxic to both cell types and one showed significant toxicity. The yellow sap from fresh aloe vera was also lethal to human fibroblasts at all tested concentrations.[150]

4.3 Phototoxicity

Exposure to products containing aloe vera extracts may lead to enhanced sensitivity to UV light, as the UVA irradiation of such extracts in the presence of methyl linoleate has been shown to produce carbon-centered free radicals and to induce lipid peroxidation.[25] Aloe emodin in particular may be responsible for the observed phototoxicity, since its incubation with human skin fibroblasts followed by UV or visible light irradiation leads to significant photocytotoxicity, accompanied by oxidative damage to both cellular DNA and RNA. The generation of singlet oxygen under UV irradiation is thought to be involved in the primary pathway through which this occurs.[26][27]

4.4 Photocarcinogenicity

Aloe emodin seems to increase the carcinogenicity of UV radiation. It weakly enhanced the photocarcinogenic activity of solar simulated light in female (but not male mice), based on an increase in the multiplicity of histopathologically-determined squamous cell neoplasms.[151] The combination of UV light, ethanol and aloe emodin has also been shown to lead to the development of primary cutaneous melanin-containing tumors in murine skin[152] and to alter the p53 mutational spectrum in UV-induced murine skin tumours.[153]

4.5 Genotoxicity

The crushed leaves of aloe vera, aloe emodin, aloesin and aloin have all tested negative in various tests of mutagenicity and genotoxicity.[154][155][156][157][158][159][160]

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