A lot of grim things can happen to a penis, from it slowly turning into bone to having a pair of tweezers lodged inside. Now, another unusual and unfortunate case has been reported in BMJ Case Reports, detailing the aftermath of a man injecting motor oil into his penis for genital augmentation purposes.

A man in Uruguay came into a Male Genital Dermatology Unit, presenting with a large “tumorous mass” that had been growing around his penile shaft for a staggering 10 years. The patient had sexual dysfunction but had no other negative symptoms stemming from the growth. Magnetic resonance imaging (MRI) scans showed that the mass was limited to the dermal and hypodermal tissues, and the growth was diagnosed as a penile sclerosing granuloma after two skin biopsies.

Penile sclerosing granuloma is a reaction to the injection of foreign bodies, mainly injected in an attempt to change the appearance of the genitals. It often presents as a “gross deformity of the penis.” These injected materials can include lipids, hydrocarbons, silicone, methacrylates, and fillers made from collagen or hyaluronic acid.

The patient reportedly “repeatedly denied any local procedures.” However, “The patient later admitted he had self-injected motor oil and declined any kind of treatment.” Presumably, due to him turning down medical care for it, he is still living with the growth.

Cases of penile sclerosing granuloma from circumstances like this have happened before. A 2010 case report discusses a man from Myanmar who injected mineral oil into his penis, having to have a skin graft phalloplasty to repair the area. Another paper from 2003 surveyed 357 men who had injected Vaseline, paraffin, or other mineral oils to increase the circumference of their penis. The data showed that many of these men were driven to inject these substances to be more “mannish”, or after a recommendation from friends who had also had penis injections.

This case is made more unusual, however, as the authors describe the growth as having an area with an iridescent rainbow pattern, “displaying the whole spectrum of the visible light spectrum.” This effect has been associated with a range of inflammatory lesions and tumors in the past, with the authors saying that the first documented example was published in 2009, in Kaposi’s sarcoma. However, this rainbow effect has never been seen before in penile sclerosing granuloma.

The authors go on to explain what they think led to this phenomenon. “We believe that this iridescent appearance is due to ‘dichroism’, produced by the interaction of polarised light with local structures, such as collagen and lipids, which have variations in their refractive index, generating changes in the reflected light that is transmitted in different wavelengths, and thus perceived as different colours,” they write in the paper.