Forty-percent of the injuries linked to electric scooter use involve knocks to the noggin while nearly 95 percent of riders don’t wear helmets, according to a first-of-its kind study published Friday, January 25.

As electric scooters and bike shares zoom into cities across the country, health experts are chasing after the potential public health and safety issues circling the micromobility market. The new study, published in JAMA Network Open, is the first to try to track the pattern of injuries linked to electric scooters.

“[M]any thousands of riders are now using standing electric scooters daily on US streets shared with millions of pedestrians and drivers,” the authors—a group of researchers at University of California, Los Angeles—write. They also note that the new transport trend is only expected to speed up, with dockless electric scooter service Lime valued at $1.1 billion and its rival Bird valued at more than $2 billion. “Therefore, understanding the impact of rising scooter use on public health is more important than ever,” the researchers conclude.