Cut an aloe leaf and two things come out. One is the clear, slippery gel most people know. The other is a thin, yellow, bitter sap that seeps from just under the green skin. That sap is aloe latex, and it behaves very differently from the gel.

This page explains what the latex is, what public health and toxicology sources say about it, and why aloe laxatives lost their over-the-counter status in the US. It sticks to what those sources state. For anything involving your own health, talk to a health care provider.

One leaf, three materials

The NIH National Center for Complementary and Integrative Health (NCCIH) says aloe products are made from different parts of the leaf: the gel from the inner leaf, the latex from the leaf’s outer layer, and whole crushed leaf, which contains both.

A review by Guo and Mei of FDA’s National Center for Toxicological Research describes the layers in more detail:

LayerWhat it is
RindThe thick outer skin
Outer leaf pulpA thin layer under the rind containing the vascular bundles. Tubules in these bundles store and carry the bitter yellow latex along the leaf margin.
Inner leaf pulpMost of the leaf by volume. Large, thin-walled cells hold the aloe gel, also called inner leaf or fillet.

So the latex sits between the skin and the gel. That is why it runs out of a cut leaf, and why care is needed to keep it off the gel.

What aloin is

The National Institute of Environmental Health Sciences (NIEHS) says aloe latex contains anthraquinones. Aloin is an anthraquinone in the latex that may give the plant its laxative qualities.

Guo and Mei identify barbaloin, also called aloin A, as the major constituent of the latex. They describe the latex as yellow-brown and bitter, with most of its compounds phenolic, mainly anthraquinone glycosides, anthrones and free anthraquinones.

What the latex does

The sources agree on the main effects of swallowing latex:

  • NCCIH: oral use of aloe latex can cause abdominal pain, cramps and diarrhea.
  • NC State Extension: aloe vera is poisonous through ingestion or dermatitis. Symptoms may include abdominal cramping, diarrhea and red urine, and skin irritation from the latex.
  • Guo and Mei: prolonged use of latex as a laxative has been associated with electrolyte imbalance from diarrhea, abdominal pain, vomiting, low potassium (hypokalemia) and pseudomelanosis coli, a darkening of the colon lining.

NCCIH adds two cautions. Overuse of aloe latex may increase the risk of adverse effects from cardiac glycosides such as digoxin. And aloe taken by mouth, whether gel, latex or whole leaf extract, may be unsafe during pregnancy and while breastfeeding. Guo and Mei note that pregnant women have been advised not to take aloe latex because its cathartic action might stimulate uterine contractions.

NCCIH also reports that oral aloe leaf extracts, taken for as little as three weeks or as long as five years, have been related to cases of acute hepatitis.

Why the FDA removed aloe from OTC laxatives

This is often described as a ban on a dangerous ingredient. The Federal Register shows it was a ruling on missing data.

  1. 1998. The FDA reclassified the stimulant laxatives aloe, cascara sagrada, bisacodyl and senna from category I (monograph) to category III (more data needed). It asked for mutagenicity, genotoxicity and carcinogenicity data on aloe and cascara sagrada.
  2. No data arrived. The 2002 rule records that the agency received data on bisacodyl and senna, but no comments or data on aloe or cascara sagrada.
  3. May 9, 2002. A final rule declared aloe (including aloe extract and aloe flower extract) and cascara sagrada not generally recognized as safe and effective, or misbranded, as OTC laxatives. They had to be removed from OTC laxative products. The rule took effect on November 5, 2002.

NCCIH summarizes it the same way: manufacturers had to remove aloe latex from OTC laxative products because of a lack of safety data. The rule also left the door open. A manufacturer could still submit new data through a new drug application.

The NTP rodent studies

Guo and Mei note that aloe vera was nominated in 1998 for carcinogenicity testing by the National Toxicology Program (NTP). The NTP’s Technical Report 577 gave rats and mice a nondecolorized whole leaf extract of Aloe vera in drinking water for up to two years. “Nondecolorized” means it had not been treated with activated carbon to remove the anthraquinones.

The NTP concluded there was clear evidence of carcinogenic activity in male and female rats, based on increased adenomas and carcinomas of the large intestine. There was no evidence of carcinogenic activity in mice. Both species showed non-cancerous changes in the large intestine.

How to read that:

  • It was whole leaf extract, latex included. NCCIH notes that most animal studies used nondecolorized whole leaf extract, which is not commonly used by consumers.
  • Aloin is suspected, not proven. NIEHS says it suspects aloin but is not sure what caused the tumours.
  • Human relevance is open. NIEHS calls the rat results cause for serious concern, and says more information on how people use aloe products is needed to judge human risk.
  • Classification. NCCIH notes that the International Agency for Research on Cancer classifies non-decolorized whole leaf extract of aloe vera as a possible human carcinogen.
  • Labels do not show aloin. NIEHS says US products are not required to state aloin content. It notes an industry self-regulated limit of 10 ppm aloin for products taken by mouth.

The gel on skin

The clear gel has a different record. NCCIH says topical aloe gel is generally well tolerated, with occasional reports of burning, itching, rash and eczema. NIEHS says applying aloe gel to the skin is not likely to cause harm. NC State says the gel can be applied to the skin and is safe for most people.

The practical risk with a home-cut leaf is the latex mixed in. NC State’s advice is short: cut away the outer part of the leaf, use only the gel, and test a small patch of skin first.

Handling a houseplant aloe safely

  • Keep latex off the gel. Remove the outer leaf layer, where the latex sits, and use only the clear inner gel. Our guide to harvesting aloe gel walks through cutting and draining a leaf step by step.
  • Wash yellow sap off skin. NC State lists skin irritation from the latex and contact dermatitis. If sap gets on your hands, rinse it off.
  • Patch test. Try a small area of skin first, as NC State advises. Stop if it burns, itches or reddens.
  • Do not eat the leaf. NCCIH and NC State both list cramps and diarrhea from ingested latex. Home-cut leaf has no aloin control at all.
  • Check with a provider first if you take digoxin or other heart medicines, or are pregnant or breastfeeding, before using aloe by mouth (NCCIH).

Pets

The ASPCA lists aloe as toxic to dogs, cats and horses. It names saponins and anthraquinones as the toxic principles. Clinical signs are vomiting (not in horses), lethargy and diarrhea. The ASPCA notes that the gel itself is considered edible.

Keep the plant where pets cannot chew it. If you think a pet has eaten aloe, call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435.

For growing the plant itself, see our aloe vera repotting guide and why aloe turns red.

References