Background

Aloe, a member of the lily (Liliaceae) family, has been used medicinally for thousands of years. Of the several hundred species, Aloe vera is the most extensively used topically. Other species such as Aloe barbadensis (Curaçao aloe) and Aloe capensis (Cape aloe) are more frequently used internally.

Uses

Aloe gel, a clear jelly-like substance obtained from the inner parenchymal tissue of the leaf, is used for topical wound healing. It has been investigated for use in wounds caused by incisions, burns, radiation, dermabrasion, frostbite, pressure, and psoriasis. The healing effect of aloe has been shown in animal models. In humans, however, clinical trials report inconsistent results. An aloe extract in hydrophilic cream improved healing of psoriatic skin lesions. Aloe gel accelerated wound healing in patients who underwent full-face dermabrasion. In patients with aphthous stomatitis, aloe did not deter the development of oral mucosal ulcers, but acemannan, a isolated aloe gel polysaccharide, accelerated healing of ulcers and reduced pain. Aloe vera gel did not prevent skin injury from radiation therapy. In patients with wounds healing by secondary intention, aloe may have been detrimental to wound healing. These inconsistent results may be explained by differences in preparations, treatment regimens, patient populations, and study methodologies.

In addition to topical administration, aloe is also taken orally. The latex of the plant, a yellow juice extracted from the superficial pericyclic cells, contains anthraquinones. Anthraquinones, particularly aloe-emodin, induce the active secretion of water and electrolytes into the lumen of the bowel. Laxative effects follow approximately 9 hours after ingestion. Oral aloe has been advocated to heal gastrointestinal ulcers, treat AIDS, lower blood sugar in patients with diabetes, treat and prevent cancer, and lower blood lipid levels. Although preliminary data suggest that aloe is potentially effective in some of these conditions, more evidence is necessary before clinicians should recommend oral aloe.

Phytochemistry and pharmacology

Aloe extract contains many compounds, not all of which have been characterized. Identified compounds include polysaccharides, lectins, anthranoids, salicylates, cholesterol, triglycerides, magnesium lactate, and carboxypeptidase. Of these compounds, the polysaccharides and lectins are the most important. Acemannan, a proprietary aloe polysaccharide, has been used in several clinical trials.

Many mechanisms have been proposed to explain the wound healing effects of aloe. The simplest of these is that aloe acts as a moisturizing agent. However, many aloe constituents are pharmacologically active, and some have anti-inflammatory effects. For example, magnesium lactate inhibits the production of histamine by blocking the enzyme histidine decarboxylase. Aloe also contains natural salicylates and other substances may inhibit the production of inflammatory mediators such as a bradykinin and thromboxane. Furthermore, aloe may have anti-bacterial and anti-viral activity. The gel polysaccharides, particularly acemannan, have immunostimulatory effects in vitro. Some constituents of aloe may have anti-mutagenic effects. Aloe may alter vascular tone, improving blood supply to wounded tissue.

Safety

The topical use of aloe is generally safe although cases of allergic dermatitis and minor burning sensations have been reported.- The internal use of aloe is contraindicated in cases of intestinal obstruction, inflammatory bowel disease, appendicitis, and abdominal pain of unknown origin. Long-term internal use can lead to electrolyte loss and dehydration and increase the risk (relative risk of 3.0) of colorectal cancer. Internal use during pregnancy or by nursing mothers is not recommended.

Preparations and dosage

Aloe is an ingredient in a wide variety of cosmetic and healthcare products. The benefits of commercially available products are unknown because many only contain minimal amounts of aloe. However, some aloe gel products are available that contain more than 95% pure aloe gel. For topical use, recommendations are to apply liberally as needed. When used internally, the typical dosage is 20-30 mg of anthraquinones/day.