Just because an ingredient is plant-derived doesn’t mean it is safe. Just ask Socrates! Poisons such as strychnine come from plants (Strychnos nux-vomica L. and other Strychnos spp.). And potent allergens, such as the heptadecylcatechols from poison oak (Toxicodendron diversilobum) and pentadecylcatedchols from poison ivy (T. radicans) are also plant derived (26).
Many plant extracts are considered safe because they are made from ingredients that are Generally Recognized as Safe (GRAS) (27). Toxicology testing is important for other extracts. Highly purified plant constituents, even if they come from plants that are GRAS, may need testing due the increased concentration of the particular constituent. Some ingredients are safe at low levels but cause problems at higher levels. Some of the types of testing that are commonly used to test the safety of cosmetic extracts include repeat insult patch testing (RIPT), cumulative irritation, in vitro mutagenicity (i. e., Ames test), in vitro cell culture methods for assessing potential ocular and/or dermal irritation (e. g., Bovine ocular assay, Irritection™, Eyetex™, Skintex™, etc.), and photosensitization. This may not be adequate in all cases.
A noteworthy example is sanguinarine, an alkaloid extracted from Bloodroot (Sanguinaria canadendid). Viadent used sanguinarine as an antiplaque ingredient in their toothpaste and mouthwash. Despite significant toxicology and clinical testing demonstrating the safety of this compound (28-37), a study was conducted by researchers at Ohio State University (38), which showed a strong correlation between the development of oral leukoplakia (potentially cancerous mouth lesions) and the use of oral products containing sanguinarine. Several follow-up studies (39-42) have confirmed this correlation. Surprisingly, other studies appear to indicate that sanguinarine may actually have potential as an anti-cancer agent (43-45). This demonstrates how complicated and confusing these safety and toxicology issues can be. Long-term safety can only be demonstrated by long-term use. When Colgate-Palmolive purchased the brand, they removed the sanguinarine.
Plant-derived compounds have the ability to deliver real benefits. Considerations in choosing a plant product should include an investigation of the status of the species (is it endangered or threatened), whether sustainable harvesting practices are being used, and whether there is a reliable source with the quantities needed. Many extraction and purification methods are used commercially depending on the desired qualities of the end product. As with all cosmetic ingredients, standard quality assurance techniques should be followed to ensure the quality and consistency of the product or extract. The safety and toxicology of the material should be investigated to eliminate or reduce the risk of harm to consumers.