Yoga clothes, along with other 'athleisure' wear, have become popular among people who are travelling, running errands or heading to routine doctor visits. Image Credit: Shutterstock

High-tech athletic clothes made with anti-odour fabrics are popular. But they also come with a little-known health hazard: The apparel may be infused with metal fibers that can cause burns in an MRI (magnetic resonance imaging).

"It's like putting your skin up against a hot plate," said Dr. Hollis Potter, chairman of the radiology and imaging department at the Hospital for Special Surgery in New York City.

Leading athletic apparel brands tout anti-odour outfits but not many people know that this feature is brought in by adding metal fibres into the fabric.

But warnings about the risk are happening on social media accounts and in some MRI scanning centers as doctors, radiology technicians and patients warn that certain high-tech stretchy workout clothes can pose a burn risk when getting an MRI.

In March, Danielle Squires, 29, of Nova Scotia, said she was getting a shoulder MRI scan following a car accident. Squires said she was already in the machine when the MRI technician stopped and noticed her leggings.

"I had to take them off because she said there might be metal in them," said Squires, who also shared her story on TikTok. "I had no idea."

All metal must be removed

Patients who get MRI scans are advised to remove jewelry and any metal from their bodies, and they are sometimes even checked with metal detectors to make sure nothing metallic accidentally enters the machines.

But depending on the reason for the scan, patients may be allowed to leave on yoga pants, socks and other clothes during the procedure. MRI experts say that many patients and technicians aren't aware that some stretchy athletic clothes, as well as masks and blankets, can contain metal fibers that aren't picked up by metal detectors.

MRI machines use powerful magnets and radio waves to produce images of your tissues, organs and skeletal system. Wearing clothing with even trace amounts of metal can interact with the magnetic field and burn skin.

Burns from textiles

As of December 2020, there have been at least six published case reports involving burns from textiles, but experts suspect many more have gone unreported.

The first reported case involved an 11-year-old girl who endured a second-degree burn while sedated during an MRI. The contents of the girl's undershirt, sold by Boston Orthotics & Prosthetics, were identified only as "Coolmax/Lycra."

It was later found that the shirt contained silver-embedded microfibers. The girl's burns corresponded with the seams of the shirt, where the silver was concentrated.

Thomas Morrissey, president and CEO of the company that sold the shirt, said the firm learned about the incident five years after it was published as a case report. A warning on the Boston Orthotics & Prosthetics website and a sticker on the packaging states that the shirt should be removed before an MRI.

Raising awareness

Jeffrey Rogg, the MRI medical director at Rhode Island Hospital who was involved in the case, said it played a critical role in raising awareness about metallic fibers: "It became evident to the community that metallic fibers aren't necessarily going to be visible or detectable."

Another case in 2019 involved a 40-year-old woman in Japan who sustained second-degree burns from jogging pants that were labeled as 100 percent polyester but apparently contained metallic fibers. Another patient suffered third-degree burns around their face and neck while wearing a mask containing metallic fibers, prompting an FDA warning in 2020.

Injuries sustained during an MRI are rare, but data shows that thermal burns are the most common, and that in about 5 percent of those cases, the burns are caused by patient clothing.

Today, you can find silver in a range of clothing, products and fabrics, including air filters, food packaging, medical devices, socks, bedsheets, underwear and even face masks. In addition to Lululemon's Silverescent fabrics, Gap's Athleta sells clothes with Ionic+ silver-infused fabric, and Patagonia sells HeiQ Pure odor-control clothing made with "silver-salt based" additives.

Athleta, Lululemon and Patagonia didn't respond to requests for comment.

Why silver?

Silver has anti-bacterial properties and can penetrate bacterial cell walls. The positive ions in silver are attracted to negative ions in bacteria, ultimately resulting in the death of the microbe, said Bryan James, a researcher at the Woods Hole Oceanographic Institution who specializes in materials science.

Experts say you can't always rely on clothing labels to tell you that a fabric contains metal fibers. Although the Federal Trade Commission requires that all clothing labels list materials used in a fabric, the rule doesn't apply to fibers that make up 5 percent or less of the fiber content.

Even trace amounts of metallic fibers can burn someone, said Michael Hoff, member of the American College of Radiology MR safety committee and director of diagnostic medical physics at the University of California at San Francisco.

"Most places are on top of this and gowning patients anyway," Hoff said. "But it's something we should be concerned about because it can cause distress to the patient, and preventable risks should be avoided at all costs."

Potter said that MRIs aren't supposed to be painful, so anyone who feels discomfort during a scan should alert medical staff right away.

Some MRI facilities may not ask you to fully gown up, either because technicians aren't aware of the potential risks metallic fibers pose or they aren't convinced the risk is serious enough, Potter said. In those cases, take your safety into your own hands and request a gown to change into.

"MR is an amazing diagnostic tool, but we have to respect the science and technology behind it," Potter said.

To lower risk, avoid wearing clothes that say "antimicrobial" or "antibacterial," experts say, because they may include metallic fibers. The safest bet is to disrobe completely and wear the gown provided by the MRI technician.

Chaundria Singleton, an MRI technician in Atlanta, has used TikTok to spread word of the risk. She said she always asks patients to remove their clothes and put a gown on.

"We don't want to waste your time and make you uncomfortable to change into our gowns," Singleton said. "We just want to make sure you're safe, and you get this test done without it harming you."