To the Editor:
Zinc chloride originally was used by Dr. Frederic Mohs as an in vivo tissue fixative during the early phases of Mohs micrographic surgery.1 Although this technique has since been replaced with fresh frozen tissue fixation, zinc chloride still is found in topical preparations that are readily available to patients. Specifically, black salve describes variably composed topical preparations that share the common ingredients zinc chloride and Sanguinaria canadensis (bloodroot).2 Patients self-treat with these unregulated compounds, but the majority do not have their lesions evaluated by a clinician prior to use and are unaware of the potential risks.3-5 Products containing zinc chloride and S canadensis that are not marketed as black salve present a new problem for the dermatology community.
A 73-year-old man presented to our dermatology clinic for the focused evaluation of scaly lesions on the face and nose. At this visit, it was recommended he undergo a total-body skin examination for skin cancer screening given his age and substantial photodamage.
Physical examination revealed more than 20 superficial, 3- to 10-mm scars predominantly over the trunk. One scar over the left mid-back had a large, 1.2-cm peripheral rim of dark brown pigment that was clinically concerning for a melanocytic neoplasm. Shave removal of this lesion was performed. Histologic examination showed melanoma in situ with a central scar. The central scar spanned the depth of the dermis, and the melanocytic component was absent in this area, raising the question if prior biopsy or treatment had been performed on this lesion. During a discussion of the results with the patient, he was questioned about prior biopsy or treatment of this lesion. He reported prior use of a topical all-natural cream containing zinc chloride and S canadensis that he purchased online, which he had used to treat this lesion as well as numerous presumed moles.
The trend of at-home mole removal products containing the traditional ingredients in black salve seems to be one of rapidly shifting product availability as well as a departure from marketing items as black salve. Many prior black salve products are no longer available.4 The product that our patient used is a topical cream marketed as a treatment for moles and skin tags.6 Despite not being marketed as black salve, it does contain zinc chloride and S canadensis. The product’s website highlights these ingredients as being a safe and effective treatment for mole removal, with claims that the product will remove the mole or skin tag without irritating the surrounding skin and can be safely used anywhere on the body without scarring.6 A Google search at the time this article was written using the term skin tag remover revealed similar products marketed as all-natural “skin tag remover and mole corrector creams.” These similar products containing zinc chloride and S canadensis were available in the United States at the time of our initial research but have since been removed and only are available outside of the United States.7
Prior reports of melanoma masked by zinc chloride and S canadensis described the use of topical agents marketed as black salve. This new wave of products marketed as all-natural creams makes continued education on the available products and their associated risks necessary for clinicians. The lack of US Food and Drug Administration oversight for these products and their frequent introduction and discontinuation in the market makes keeping updated even more challenging. Because many patients self-treat without prior evaluation by a health care provider, treatment with these products can lead to a delay in diagnosis or inaccurate staging due to scars from the chemical destruction, both of which may have occurred in our patient.5 Until these products become regulated by the US Food and Drug Administration, it is imperative that clinicians continue to educate their patients on the lack of documented benefit and clear risks of their use as well as remain up-to-date on product trends.