Canadian Jenn Marr was undergoing a Magnetic Resonance Imaging (MRI) in 2014 when she felt a burning sensation on her lower extremities 15 minutes into the scan. It got so bad she had to press the emergency stop button and be pulled out of the machine.

She was wearing yoga pants sold by Vancouver, Canada-based retailer Lululemon, that were manufactured with their “Silverescent” technology. The technology incorporates silver-bonded threads that claims to inhibit the growth of odor-causing bacteria.

A similar occurrence happened to an 11-year-old girl who was sedated during the MRI, but when she woke up, second-degree burns were found on parts of her body. It was eventually determined to have been caused by silver microfibers in her undershirt.

“Patients can be burned because of a similar reaction that occurs during induction cooking,” explains Haifang Li, an image scientist at the Stony Brook School of Medicine. “Metal produces extra heat in a magnetic field.”

MRI Screening Process and Metal in Clothes

Medical professionals who prepare patients for an MRI have always asked them to remove all metal from their bodies or clothes before entering the MRI chamber. This specific type of risk is relatively new and more radiologists have banned athleisurewear within the last five years.

MRI machines use radio waves and electromagnetism that turns the unit into a powerful magnet.

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Mount Sinai and Stony Brook University’s hospitals in New York are two of the major hospital systems that recently changed their policies from allowing patients to wear stretch clothing to mandating they wear paper gowns or cotton T-shirts before undergoing an MRI.

“I suspect many patients are unaware of the clothing risks associated with these types of popular activewear,” says Bradley Delman, associate professor, Radiology, Mount Sinai Hospital. “Even very comfortable clothing can present unnecessary risks. A patient’s safety is priority one.”

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One problem consumers may unknowingly encounter is so many retailers use proprietary marketing names to brand their products. It is almost impossible for all consumers to keep up with fabric content names and terms. “Unless you’re a careful consumer and read product labels when shopping, you might not know the fabric content of your clothes,” says Alison Matthews David, assistant professor, Ryerson University, Toronto, Canada. “Wear your good, old-fashioned T-shirt and sweatpants.”

“Our hospitals have not seen this happen but are aware of this issue and have taken precautions to thoroughly prepare and protect our patients before they enter the MRI chamber,” said Valerie Burrow, Baptist Hospitals, Memphis, Tenn.