Aloe vera has been hailed as beneficial for everything from minor burns to irritable bowel syndrome. Products containing aloe vera have been the basis for many businesses and even home parties where the products are sold. Hailed as safe, pleasant, inexpensive, and readily available, it has been suggested that every kitchen in America should have an aloe vera plant growing on the windowsill—just in case.

One of more than 250 different aloe species, aloe vera is native to northern Africa.1 It is a stemless succulent that grows as tall as 100 cm. The leaves grow in a rosette distribution and are lanceolate, thick, fleshy, and grayish-green with a distinctive serrated margin.

Each plant typically has 12-16 leaves that may each weigh as much as 3 lb when mature. The plants can be harvested every six to eight weeks by removing three to four leaves per plant.2 Flowers are produced annually in the spring on a spike up to 90 cm tall. The flower itself is pendulous with a yellow tubular corolla 2-3 cm in length.1

Aloe vera is easily cultivated in frost-free climates.1 It has become a common component of ornamental gardens and among houseplants. Well-drained soil and adequate protection from cool temperatures will help ensure success. In the United States, most commercial aloe vera is grown throughout Florida, southern California, and the Rio Grande Valley of southern Texas. Though it resembles a cactus, it is actually a member of the tree lily family. As such, it is more closely related to such plants as garlic, onion, and turnip.2 The flower structure and appearance make the association with the lily family more obvious.

Background

The original commercial use of the aloe plant was in the production of a latex substance called aloin, a yellow sap used for many years as an ingredient in laxatives. This product and its role as a source of aloe became popular in technical and government literature during the early 20th century. In the early 1950s, aloe vera gel became popular as a base for nutritional drinks, moisturizer, and topical healing agent in cosmetics.2

Aloe has also been studied as a food preservative (e.g., sprayed on grapes to prolong freshness for more than a month).1

Mechanism of action

Chemical analysis reveals that aloe vera gel contains amino acids, minerals, vitamins, enzymes, proteins, polysaccharides, and biological stimulators.2 These chemical components function in a wide variety of ways. Combinations of anti-inflammatory, immune-modulating, and moisturizing activity seem to be responsible for the purported healing properties.

Aloe vera’s anti-inflammatory action is believed to result from a thromboxane A2 blockade, which inactivates bradykinin and inhibits prostaglandin A2 and oxidation of arachidonic acid. A purported antipruritic effect is due to blocked conversion of histidine to histamine as a result of the inhibition of histidine decarboxylase. Aloe’s wound-healing properties are believed to be attributable to increased blood flow to the area, which is caused by interference with the proconstrictive chemicals in the thromboxane cascade.3

In a Cochrane Database review, no clinical trials have shown efficacy for some of the other more notable claims for aloe vera. Moderation of glucose levels in diabetes mellitus, improvement of lipid profiles, and treatment of gastric problems (such as constipation) have not been supported by studies. There are anecdotal data suggesting that oral use of aloe vera can lower blood sugars,4 so diabetics using insulin or oral hypoglycemics should avoid it.

The two areas in which well-conducted clinical trials have shown positive benefit are treatment of psoriasis and speeding healing of genital herpes outbreaks. In one randomized, controlled clinical trial pitting aloe vera gel against placebo for psoriasis, skin eruptions of the aloe subjects healed in 83% of cases (compared with 7% on placebo).5 A similar trial for acute genital herpes outbreaks showed equally impressive healing results.5 Another trial using aloe gel to treat acne vulgaris showed 90% healing of lesions at five days, compared with only 40%-50% of placebo-treated lesions.5

Typical household usage of a freshly severed aloe vera leaf for minor burns is only mildly supported by literature, with no statistical significance found. Oral use of aloe vera can cause nausea, cramping, and diarrhea with dependency potential if used for seven days or longer.5

Dosage, manufacturing, and how supplied

Pure aloe gel mechanically extracted from the succulent fleshy leaves is often applied liberally to skin. Those who are attempting to standardize the quality of aloe gel extracts recommend that they contain 0.5% by weight of a 50% ethanol extract of aloe, combined with mineral and castor oils.4 Pure aloe gel, unless pasteurized, spoils quickly at room temperature and should be refrigerated. For psoriasis and herpes genitalis, this cream compound should be applied three times daily for five consecutive days per week for up to four weeks.2

Safety

Those with known allergy to garlic, onions, tulips, or other plants of the Liliaceae family may have allergic reactions to aloe. Although topical use is unlikely to be harmful during pregnancy or breastfeeding, oral use is not recommended because aloe may stimulate uterine contractions. Whether active ingredients of aloe may be present in breast milk is unknown.4

Summary

Though relatively inexpensive and harmless, aloe vera products have not, in most cases, been proven to be the panacea that health-food advertisements would have you believe. For psoriasis, genital herpes, and acne vulgaris, use of topical compounds is an appropriate recommendation after skin patch testing for allergic reaction. Oral use should not be recommended. The common household use for minor burns and skin irritations, while not proven effective, is not harmful. Patients should be educated regarding when a wound needs further attention.

Ms. Sego is a staff clinician at the Veterans Administration Hospital in Kansas City, Mo., where she practices adult medicine and women’s health. She also teaches at the nursing schools of the University of Missouri and the University of Kansas.

References

1. Wikipedia. Aloe vera. Available at http://en.wikipedia.org/wiki/Aloe_vera. Accessed February 5, 2008.

2. The International Aloe Science Council. The complete story of aloe vera. Available at www.iasc.org/aloe.html. Accessed February 5, 2008.

3. Fetrow CW, Avila JR. Professional’s Handbook of Complementary & Alternative Medicines. Springhouse, Pa.: Springhouse Corp; 1999:26.

4. MedlinePlus. Aloe (Aloe vera). Available at www.nlm.nih.gov/medlineplus/druginfo/natural. Accessed February 5, 2008.

5. Vogler BK, Ernst E. Aloe vera: a systematic review of its clinical effectiveness. Br J Gen Pract. 1999;49:823-828.