Aloe vera

Aloe vera is a succulent with no obvious stem (or a very short one), forming dense clumps through offsets around the base. Leaves are arranged in a rosette, thick and succulent, 30–60 cm long and 4–8 cm wide, grey-green and often covered by a waxy bloom, with soft spiny teeth along the margins and a slightly concave surface. Each leaf has three layers: the outer rind, a yellow latex layer rich in bitter anthraquinones, and the clear inner gel rich in polysaccharides. Under favourable conditions it flowers in winter–spring on a 60–90 cm spike bearing many yellow tubular flowers.

According to Kew's Plants of the World Online, Aloe vera is native to the Hajar Mountains of northern Oman on the Arabian Peninsula, in desert and dry-shrubland vegetation. From there it spread across the tropics and subtropics and has naturalised around the Mediterranean, the Middle East, Asia, the Americas and the Caribbean. Today it is grown commercially on a large scale in India, China, Mexico, the Dominican Republic, North Africa, Southeast Asia and southern Europe for gel, cosmetics and beverages.

The clear gel makes up most of the leaf mass and is about 99% water; the dry matter is dominated by polysaccharides, notably acemannan (an acetylated mannan) together with glucomannan, arabinogalactan and galactogalacturan. The yellow latex between rind and gel contains bitter anthraquinones — aloin A/B (barbaloin), aloe-emodin and emodin — plus chromones such as aloesin and aloeresin A. The gel also holds amino acids, enzymes (for example bradykinase), vitamins and minerals, while the leaf carries organic acids and phenolics. Acemannan and aloin levels vary with cultivar, plant age, harvest season and gel-extraction method.

A review by Sánchez et al. (Molecules, 2020) and more recent assessments summarise Aloe vera's pharmacology: wound- and burn-healing support, anti-inflammatory, immunomodulatory, antioxidant, antimicrobial, antihyperglycaemic and (mainly in-vitro) anticancer effects. Acemannan stimulates macrophages to release cytokines and is licensed as a veterinary biological response modifier; aloesin inhibits tyrosinase (a skin-lightening aid), while aloin and aloe-emodin show anticancer cytotoxicity but are also the stimulant-laxative constituents. Practically, the gel is applied topically to soothe skin and blended into creams, cleansers and beverages, while the dried latex is the traditional laxative drug aloe.

On safety, the laxative anthraquinones of the latex are suspected of toxicity and genotoxicity with prolonged use; since 2002 the US FDA has required removal of aloe-containing laxative products, and the European Union restricts hydroxyanthracene derivatives (aloin) in food. Aloin-stripped gel is generally considered safe for topical use, but oral use and use in pregnancy warrant caution. On the IUCN Red List Aloe vera is Not Evaluated (NE) and is not listed by CITES; it is widely cultivated and not threatened, although many other wild Aloe species in the Arabian Peninsula and Madagascar face harvesting and habitat loss.