A bogus cancer medicine has left an Australian man with a hole burnt in the side of his head, prompting renewed warnings for cancer patients to avoid alternative therapies.

A 55-year-old man recently presented to a Brisbane hospital with a black hole in his temple after applying an unproven alternative medicine known as "black salve" to a lesion on his face, which he believed was cancerous.

Black salve's dangers are evident in this picture. A hole is clearly visible in the side of the subject's head.

Writing in the Med-ical Journal of Australia, doctors from the Princess Alexandra Hospital said the man had been applying the unlicensed product, which is sold online as an alternative skin cancer treatment, to his face for four months.

The doctors, Natalie Ong, Eric Sham and Brandon Adams, said black salve preparations often contained an alkaloid derived from bloodroot and zinc chloride which could both eat away at tissue, leading to significant scarring and disfigurement.