Aloe vera is one of the most widely recognized medicinal plants in the world and, arguably, one of the most commonly used within the vast landscape of natural health products. Its presence is ubiquitous in skin creams, cosmetic formulations, functional beverages, dietary supplements, and a wide range of wellness products marketed globally. Much of this popularity stems from the perception that Aloe vera is a natural ingredient associated with healing, soothing, and general well-being. Many people use it to treat minor burns, skin irritation, digestive discomfort, or simply as part of daily personal care routines. However, from a scientific perspective, any substance capable of exerting biological activity in the body can also produce adverse effects depending on factors such as dosage, method of consumption, and chemical composition. As the global consumption of herbal products has expanded, researchers have increasingly turned their attention to studying Aloe vera not only for its potential benefits but also for the biological effects that some of its compounds may have on human health.
Aloe vera is not a single chemical entity but rather a plant with a remarkably complex biochemical composition. Its leaves contain a wide variety of molecules, including polysaccharides, phenolic compounds, vitamins, minerals, enzymes, and several classes of bioactive phytochemicals capable of interacting with different physiological systems. This chemical diversity partly explains why Aloe vera has been the focus of extensive scientific investigation over the past several decades. Some studies have identified properties that may support wound healing, hydration of the skin, and anti-inflammatory responses when applied topically. At the same time, deeper analysis of the plant’s composition has revealed that certain fractions of the leaf contain compounds with much stronger biological activities. Among these compounds are a group of molecules known as anthraquinones, which have attracted considerable attention in toxicological and biomedical research because of their ability to interact with fundamental cellular processes.
Anthraquinones are primarily found in a layer of the Aloe leaf known as the Aloe latex, a yellowish substance located just beneath the outer rind of the plant. Some of the best-known anthraquinones in Aloe include aloin, aloe-emodin, and emodin, molecules that historically contributed to the plant’s use as a natural laxative. These compounds stimulate intestinal motility and promote water secretion in the colon, which explains why Aloe extracts were traditionally used to treat constipation. Yet the scientific interest in these molecules extends far beyond their gastrointestinal effects. Research over the past decades has shown that anthraquinones possess significant biological activity and can influence cellular mechanisms involved in processes such as oxidative stress responses, cell proliferation, and the maintenance of genomic stability. These mechanisms are highly relevant in the context of cancer biology, because disruptions in DNA integrity or abnormal regulation of cell growth are central features of tumor development.
The potential link between certain Aloe compounds and carcinogenic processes began to attract particular attention when experimental studies reported that some anthraquinones could produce cytotoxic and genotoxic effects in laboratory models. In cellular systems, these compounds have been observed to influence cell viability and, under certain experimental conditions, interact with genetic material. While findings from in vitro studies do not necessarily translate directly to effects in humans, they raised important questions about how these molecules might behave in complex biological environments. Because DNA damage and alterations in cell cycle regulation are key mechanisms involved in cancer initiation and progression, these observations prompted researchers to explore the issue further.
Scientific concern increased significantly following a series of long-term animal studies that evaluated the biological effects of prolonged exposure to Aloe extracts. In several of these experiments, researchers administered whole-leaf Aloe vera extracts, which include both the inner gel and compounds present in other parts of the leaf, including anthraquinones. The findings were striking: animals exposed to these extracts for extended periods developed tumors in the large intestine, particularly in the colon. These results generated substantial scientific debate because they suggested that some components of whole-leaf Aloe preparations might possess carcinogenic potential under specific experimental conditions.
The implications of these findings prompted international health organizations to examine the available evidence more carefully. One of the most influential assessments was conducted by the International Agency for Research on Cancer (IARC), a global authority responsible for evaluating the carcinogenic potential of various substances. After reviewing the experimental data, IARC classified whole-leaf Aloe vera extract as “possibly carcinogenic to humans” (Group 2B). This category is used when there is sufficient evidence of carcinogenicity in experimental animals but limited or inadequate evidence in human populations.
Importantly, the Group 2B classification does not mean that Aloe vera has been proven to cause cancer in humans. Instead, it indicates that the available data suggest a potential risk that warrants careful scientific consideration and further investigation. Many substances encountered in everyday life fall into this same category, often because animal studies have demonstrated carcinogenic effects under conditions that may not fully replicate typical human exposure.
Researchers have proposed several biological mechanisms that might explain the observations reported in experimental studies. One hypothesis centers on the ability of certain anthraquinones to generate oxidative stress, a condition in which reactive oxygen species accumulate and damage essential biological molecules such as lipids, proteins, and DNA. Persistent oxidative stress can increase the likelihood of genetic mutations, particularly when cellular repair systems are unable to correct the damage efficiently. Over time, the accumulation of such mutations may contribute to the development of cancer.
Figure 1. The main fractions of the Aloe vera leaf, including the inner gel and the Aloe latex, which contains anthraquinone compounds such as aloin, aloe-emodin, and emodin. These molecules may increase oxidative stress in cells, potentially leading to DNA damage and alterations in normal cell growth regulation.
Another potential mechanism involves the interaction of anthraquinones with cell cycle regulation, the tightly controlled process that determines when cells divide, pause, or undergo programmed cell death. Disruptions in this regulatory system can allow damaged cells to survive and proliferate, increasing the probability that abnormal cell populations may eventually evolve into tumors. Some experimental studies have suggested that certain anthraquinone derivatives may influence these regulatory pathways, although the exact molecular mechanisms remain an active area of research.
It is also important to recognize that the type of Aloe preparation plays a crucial role in determining its biological effects. Many of the studies that observed carcinogenic outcomes used whole-leaf extracts, which contain a mixture of compounds including significant concentrations of anthraquinones. In contrast, the purified inner gel of Aloe vera — the fraction most commonly used in dermatological and cosmetic products — contains much lower levels of these molecules.
As scientific awareness of these issues has grown, many manufacturers have implemented industrial processes designed to remove or significantly reduce anthraquinones from Aloe-derived products intended for human consumption. These purification methods aim to retain beneficial polysaccharides from the gel while minimizing exposure to compounds that may have undesirable biological effects.
The case of Aloe vera illustrates an important principle in biology and toxicology: natural origin does not automatically guarantee safety. Many plant-derived molecules possess powerful biological activities, which explains both their medicinal potential and the need to study them rigorously. In the case of Aloe vera, modern research has revealed that the plant contains compounds capable of interacting with cellular pathways that are closely linked to cancer biology.
Understanding these interactions remains an ongoing challenge for biomedical science. As new studies continue to explore the molecular behavior of Aloe-derived compounds, researchers hope to clarify under what conditions, doses, and forms of exposure certain components of the plant might pose health risks. At the same time, these investigations highlight the importance of applying the same scientific scrutiny to natural products that is routinely applied to conventional pharmaceuticals. Only through careful research can we ensure that the widespread use of plant-based remedies is both informed by evidence and aligned with long-term health safety.
Main reference:
Guo, X., & Mei, N. (2016). Aloe vera: A review of toxicity and adverse clinical effects. Journal of environmental science and health. Part C, Environmental carcinogenesis & ecotoxicology reviews, 34(2), 77–96. https://doi.org/10.1080/10590501.2016.1166826
Other references:
Cosmetic Ingredient Review Expert Panel (2007). Final report on the safety assessment of AloeAndongensis Extract, Aloe Andongensis Leaf Juice,aloe Arborescens Leaf Extract, Aloe Arborescens Leaf Juice, Aloe Arborescens Leaf Protoplasts, Aloe Barbadensis Flower Extract, Aloe Barbadensis Leaf, Aloe Barbadensis Leaf Extract, Aloe Barbadensis Leaf Juice,aloe Barbadensis Leaf Polysaccharides, Aloe Barbadensis Leaf Water, Aloe Ferox Leaf Extract, Aloe Ferox Leaf Juice, and Aloe Ferox Leaf Juice Extract. International journal of toxicology, 26 Suppl 2, 1–50. https://doi.org/10.1080/10915810701351186
Rodríguez Rodríguez, E., Darias Martín, J., & Díaz Romero, C. (2010). Aloe vera as a functional ingredient in foods. Critical reviews in food science and nutrition, 50(4), 305–326. https://doi.org/10.1080/10408390802544454
Boudreau, M. D., & Beland, F. A. (2006). An evaluation of the biological and toxicological properties of Aloe barbadensis (miller), Aloe vera. Journal of environmental science and health. Part C, Environmental carcinogenesis & ecotoxicology reviews, 24(1), 103–154. https://doi.org/10.1080/10590500600614303
