Aloe vera: what the evidence says

The gel inside aloe leaves has been used for thousands of years to treat wounds, skin inflammation, burns and other skin conditions, and the dried inner layer of the leaf (aloe latex) has been taken by mouth as a laxative.

There is strong scientific evidence for aloe's laxative effect, which comes from the anthraquinone glycosides in the leaf skin, but it hasn't been well compared with other laxatives. Laboratory, animal and human studies suggest aloe gel may affect the immune system and help heal skin inflammation.

Uses with scientific evidence

Constipation (grade A, strong evidence): aloe latex is laxative because of its aloin content, but its dose and safety haven't been studied well enough.
Seborrhoeic dermatitis and dandruff (grade B, good evidence): in one study a 30% aloe lotion applied daily for 4–6 weeks helped, but more studies are needed.
Psoriasis (grade B): a cream containing 0.5% aloe extract was effective in a clinical study, but more research is needed.
Genital herpes (grade B): in men, a 0.5% aloe extract cream worked better than aloe gel or a placebo, but more research is needed.
Burns (grade C, unclear evidence): studies suggest aloe may help mild to moderate burns, but they were of poor quality.
Radiation skin reactions (grade C): results are unclear.
Mouth ulcers (grade C): two human studies suggest aloe eases pain and lengthens the time between ulcers.
Diabetes (grade C): aloe lowered blood sugar in mice and in two human studies, but a third study found no effect.
HIV (grade C): aloe gel stimulated immunity in the lab, but study results were mixed.
Cancer prevention (grade C): one small study suggested oral aloe might lower the risk of lung cancer.
Stress ulcers and surgical wound infections (grade D): weak evidence suggests aloe may not work, and on surgical wounds it slowed healing.

Many other uses rest only on tradition or theory, from baldness, arthritis and asthma to high cholesterol, heart failure, kidney stones and parasites, and have not been proven.

How it is used

Pure aloe gel can be applied directly to the skin, and many skin products contain aloe alone or with other ingredients. Applying aloe gel to the skin is common in children and is usually well tolerated. Aloe must never be injected: four deaths have been reported after aloe injections.

Safety

Allergy: people allergic to garlic, onions or other plants of the lily family may react to aloe, and long-term use of the gel can cause hives or an eczema-like rash.
Skin: aloe slowed the healing of surgical wounds, and applying it before sun exposure may cause redness.
By mouth: aloe latex can cause diarrhoea and cramps, and low blood potassium, which can cause abnormal heart rhythms and muscle weakness, especially with diabetes, kidney disease, heart disease, diuretics such as furosemide, steroids, digoxin, liquorice or other laxatives. Using it for more than a week can cause dependence, and long-term use may raise the risk of bowel cancer. It shouldn't be taken by people with severe abdominal pain or bowel obstruction.
Blood sugar: oral aloe may lower blood sugar and strengthen the effect of diabetes medicines and insulin.
Pregnancy and breastfeeding: using aloe on the skin is fine, but it shouldn't be taken by mouth.

Update: in 2002 the US FDA removed aloe from over-the-counter laxatives because its safety had not been shown, and whole-leaf aloe extract has been found to cause cancer in animal studies. Aloe gel on the skin remains widely used and is generally safe.