(NEXSTAR) — If you’ve been watching the FIFA Women’s World Cup, you may have noticed a player or two wearing horseshoe-shaped collars around their necks. Since necklaces and jewelry are prohibited in soccer, what could they possibly be?

This isn’t the first time we’ve seen athletes sporting the collars — multiple NFL players began wearing them this year, while others have been wearing them as far back as 2016.

Known as a Q-Collar, the device is intended to protect athletes’ brains during head impacts. The Food and Drug Administration authorized the marketing of Q30 Innovations’ Q-Collars in 2021, saying they “may reduce the occurrence of specific changes in the brain that are associated with brain injury.”

If you are hit in the head or body, you may suffer a traumatic brain injury, known as a TBI. A leading cause of TBI is blunt trauma accidents, which are among the most common in sports, according to the National Institute of Neurological Disorders and Stroke.

During one of these incidents, your brain will typically move in the skull unrestrained, the FDA explains. This is known as a “slosh.”

According to the FDA, the Q-Collar compresses against the jugular veins in the athlete’s neck, increasing the volume of blood in their skull’s blood vessels. The increased blood then creates “a tighter fit of the brain inside the skull,” which could reduce the “slosh.”

It isn’t just NFL players that have opted for the device. Canada’s Quinn was seen wearing a Q-Collar during the team’s match against Nigeria last week.

Don’t be surprised if you see more players in the Women’s World Cup wearing the collars. Research has found that female soccer players are twice as likely to suffer concussions as their male counterparts. A study published in 2019 that tracked concussions reported among high school athletes found girls’ soccer had the second-highest rate of concussions, coming in slightly behind boys’ football. The U.S. Soccer Federation even implemented a policy in 2015 that banned heading the ball for players 10 years old and younger.

The Q-Collar trend doesn’t end with athletes. Last fall, the U.S. Army Medical Research and Development Command awarded Q30 Innovations a $2.8 million contract to fund research and development of the Q-Collar to determine if it can reduce blast-induced TBIs among soldiers.

The FDA did, however, warn in its 2021 authorization that Q-Collars shouldn’t be used by athletes with certain conditions and can’t prevent concussions or serious head injuries. Even former Carolina Panthers linebacker Luke Kuechly suffered a concussion in the weeks after he began wearing the Q-Collar.

Adil Hussain, D.O., a physical medicine and rehabilitation doctor who specializes in brain injury medicine at Rancho Los Amigos National Rehabilitation Center in California, told ABC News after the FDA’s authorization that, in theory, the Q-Collar works like a seat belt for the brain.

But Hussain and other experts expressed concerns that athletes may overestimate the device’s ability to prevent concussions or more severe brain injuries — something that hasn’t been supported by research.

The FDA expressed its own concerns in October 2022, citing uncertainty about part of the study that led to the Q-Collar’s approval in a summary of its decision, The New York Times reports. The study emphasized the difference in brain tissue changes detected in scans for athletes wearing the collar versus those that weren’t, claiming those that did wear the collar had fewer changes. The FDA said the link between changes in study participants’ brain tissue and real brain injuries had yet to be “validated.”

Experts speaking with the outlet noted that while the idea of protecting the brain from inside the skull is worthwhile, studies supporting the Q-Collar’s effectiveness aren’t. They pointed to the data in the study as not making sense and that the scans are difficult to interpret, adding that few conclusions could be drawn based on the results. Even Q30 Innovations acknowledges additional research is needed to determine the benefits the collar can provide.

Still, you can expect to see athletes across multiple sports wearing the collars. Q30 lists multiple athletes as its ambassadors on its site, including Portland Thorns midfielders Rocky Rodriguez and Meghan Klingenberg, Dallas Cowboys running back Tony Pollard, Philadelphia Eagles running back Boston Scott, and retired Pro Bowler Vernon Davis.