A 23-year-old man in Chicago developed a rare, festering fungal lesion on his lower lip after he reportedly “snipped a pimple” with a woodworking blade.

Doctors at the John H. Stroger Jr. Hospital of Cook County treated the man, who was an otherwise healthy construction worker. In a case report, recently published in The Journal of Emergency Medicine, the doctors described the lesion as a blood-crusted, warty plaque with a hardened border. It spanned the width of his mouth and had erupted just below his lips. You can see it here, but warning: it’s really gross.

The man reported that it had developed over the course of seven months, after he took the woodworking tools to what he called a pimple (although it’s possible it was any type of skin lesion, including a canker or cold sore).

A skin biopsy revealed a rare, budding yeast form growing in the lesion. Further fungal culturing identified it as Blastomyces conidia, fungi that tend to live in soil and wet, decaying wood in areas around waterways. It’s known to cause infection—called blastomycosis—in humans and animals. However, the vast majority of cases present as lung infections, likely caused by people kicking up and inhaling spores, usually from soil. In these cases, the infection may go undetected or cause mild, flu-like symptoms. But if the infection spreads to the blood, similar warty lesions can pop up on the skin and elsewhere.

The construction worker’s lesion wasn’t linked to a lung infection, however. His chest X-rays were clear, and he had no other symptoms. Instead, doctors suspect he directly infected his skin with the dirty woodcarving blade, which could easily have been contaminated with spores.

Doctors have recorded fewer than 50 such direct skin infection cases in the medical literature.

However gross, the infection is luckily treatable. Doctors gave the man an anti-fungal medication and the lesion was significantly cleared up in two weeks.

Popping zits is generally not a great idea, dermatologists warn. You run the risk of making a pimple more inflamed and painful, creating scars, and spurring skin infections. But, if you really must pop an over-ripe pimple, at least don’t do it with dirty carving tools.

The Journal of Emergency Medicine, 2017. DOI: 10.1016/j.jemermed.2017.09.034  (About DOIs).