A penis of man started turning black after his partner accidentally bit it during sexual intercourse and a black wound immediately began spreading across the head, a new case study has revealed.

According to the study, published in the Visual Journal of Emergency Medicine, the unidentified 43-year-old man from the US went to the hospital when he noticed the wound was getting darker and the pain was getting increasingly worse.

“Approximately five days prior, his significant other accidentally bit him on the tip of the penis during sexual intercourse,” study lead author Marc Zosky from the University of Arizona in the US, was quoted as saying by nypost.com.

“Since the initial trauma, the patient noted the wound to be worsening in pain and became darker,” Zosky added.

According to the study, on examination, there was 3cm of black tissue on the end of his member was present and It had become necrotic and the skin was starting to rot.

Doctors admitted the man to the hospital, where the urology and infectious disease teams both took a look at his blackening tool and quickly treated him with intravenous antibiotics, the nypost.com reported.

There were no drainage issues associated with the wound and the man was later discharged with an oral antibiotic prescription, the study said.

“As in this case, patients who are bitten on the penis often do not seek immediate medical care, and the disease process often progresses. Progression to skin ulceration and infection is common and requires careful wound care and antibiotic therapy,” said the researchers.

In rare cases, bites can lead to life-threatening infectious such ulcers – and potentially lethal gangrene, that requires emergent surgical treatment, they added.