Black salve composition: An evaluation of the potential for normal tissue toxicity and treatment failure from black salve products

Black salve, used as an alternative skin cancer therapy, contains both herbal and chemical constituents, including extracts of the rhizomes of Sanguinaria canadensis and zinc chloride. Black salves may be ordered online and have been associated with cases of extensive tissue necrosis and treatment failures that have resulted in patient fatalities. Despite these adverse outcomes and continued use by patients, black salve products have not been quantitatively assessed to determine their constituent concentrations. Thirteen different black salve products from eight manufacturers were analysed using validated HPLC-MS and ICP-MS methods to assess S. canadensis alkaloid and zinc chloride concentrations. This analysis revealed a dramatic variation in constituent concentrations between manufacturers of black salve products. The alkaloid sanguinarine was found at concentrations significantly exceeding the cytotoxic IC50 of normal human epidermal keratinocytes in the majority of black salve products, with one black salve examined having a concentration 900 times the IC50 level. The majority of products contained zinc chloride at concentrations known to kill normal human tissue, while one black salve product was found to contain an elevated lead level of 258 ppm, which exceeds the 10 ppm FDA determined lead limit for cosmetic products. Whilst some of the black salve products were found to contain high concentrations of constituents cytotoxic to normal tissue, others were found to contain insufficient cytotoxic constituents to be reasonably expected to exert any anti-cancer activity. In their current formulations, the majority of black salves analysed pose a significant risk of harm to patients and should not be available for unregulated clinical use. Further black salve toxicity testing is urgently required.