Black salve / escharotic paste

That a bloodroot and zinc chloride paste selectively destroys cancerous tissue and pulls the tumour out whole, leaving healthy skin untouched.

Descends from nineteenth-century escharotic cancer treatments, revived through alternative-medicine mail order and, since the 2010s, sold heavily on social platforms with graphic before-and-after imagery. The dramatic scab that detaches is the marketing.

Zinc chloride is an indiscriminate corrosive. It has no ability to distinguish tumour from healthy tissue; the visible "tumour coming out" is a necrotic plug of whatever tissue the paste reached. Dermatology journals carry a steady stream of reconstructive case reports. The specific danger beyond disfigurement is that the surface wound heals over residual malignant cells, so a patient believes the cancer is gone while it progresses underneath, presenting later at a far worse stage.