After experts warned people about the potentially lethal bee sting therapy, another animal-based treatment has been linked to health risks in a new case study.

Following a fish pedicure session, an unnamed woman experienced abnormalities in her toenails and eventually saw them fall off. In other words, definitely stick to the old-fashioned foot massage and nail polishing when you book your next appointment at the nail salon.

The report titled "Onychomadesis Following a Fish Pedicure" was published in JAMA Dermatology on July 3.

So, what exactly is a fish pedicure?

This kind of pedicure simply involves a species of fish known as Garra rufa. As a part of the treatment, a person immerses their feet into a tub of water filled with these small aquatic animals.

The "doctor fish," as they are also known as, will begin to eat dead human skin since they are not given access to any plant-based sources of food. "Fish pedicures peaked in popularity about 10 years ago and are still trending today," wrote Dr. Shari Lipner, a dermatologist at Weill Cornell Medicine.

"Their attractiveness was likely due to unfounded claims that the treatment would leave feet smoother and smelling fresher, increase circulation, eliminate fungus and bacteria, and treat psoriasis and eczema."

What happened to the woman from the new report?

The female patient in her 20s presented a case of "abnormal toenails," despite the lack of injury, nail disorders, major illnesses, use of medications, etc. But she did remember getting a fish pedicure a few months before the start of the nail abnormalities. 

After examination, the doctor diagnosed her with onychomadesis — when the nail stops growing and eventually falls off. Lipner stated that this was, to her knowledge, the first case of onychomadesis associated with a fish pedicure.

Exactly how it happened is not clear, but the authors suspected that the fish bites may have affected nail plate production in some way. Fortunately for the patient, the condition is likely to resolve itself as the nail is expected to naturally grow back within 18 months or so.

Any other possible risks to know about?

Doctors generally do not recommend fish pedicures for a number of reasons. There is a hygiene problem as both the animals and the tub cannot be disinfected or sanitized between sessions. So there is a risk of passing on infections from one customer to another, especially when someone has cuts or sores on their feet.

The treatment is performed at a salon, not provided by medical professionals. If the wrong species of fish is used (such as the Chinese Chinchin which closely resembles Garra rufa), they may cause injury and even draw blood. 

Due to these health risks and animal cruelty concerns, fish pedicures have been banned in more than 10 American states and parts of Europe.