In high school sports played by both girls and boys, girls are about 50 percent more likely to get a concussion, according to a recent U.S. study.
The reasons may have to do with physical or equipment differences and how often girls and boys report concussions they experience, but the result indicates a need for more research and better prevention strategies, researchers say.
"Parents and athletes alike should be active participants in concussion prevention," said senior study author Dr. Zachary Y. Kerr from University of North Carolina at Chapel Hill in North Carolina.
"This needs to include more than just reviewing concussion fact sheets. This should include advocating to their high schools the importance of having concussion education and prevention programs that can help mitigate the incidence and severity of concussion," he said by email.
Nearly 8 million U.S. high school students participate in sports every year, with more than 2 million competing in the sports where concussion is common: football, ice hockey, lacrosse and soccer, the study team writes in Journal of Athletic Training.
Kerr's team used information from the National Athletic Treatment, Injury and Outcomes Network (NATION) surveillance program to determine concussion rates in 27 sports at 147 high schools in 26 states between 2011 and 2014.
Overall, there were nearly 4 sports-related concussions per 10,000 participations in practices or competitions, with the highest rates in football (9.21 concussions per 10,000 participations), boys' lacrosse (6.65 per 10,000) and girls' soccer (6.11 per 10,000).
Concussion rates were more than three times as common in competitions as during practice.
There were no reported concussions in boys' crew, cross-country, golf, swimming and diving or in girls' golf.
Player-to-player contact was the most common cause of concussion injury and accounted for about 60 percent of concussions in boys and about 40 percent in girls.
Among the many sports in which both sexes participated, including baseball, softball, basketball, crew, cross-country, lacrosse, soccer and others, sport-related concussion rates averaged 56 percent higher in girls than in boys.
In baseball and softball, girls' concussion rate was four times that of boys.
Some recent research has shown that boys are less likely than girls to report concussion symptoms, which could be one explanation for the disparity, the authors note.
In addition, while player-to-player contact was the most common cause of concussions across the board, among just the girls, the biggest cause was player contact with equipment.
The authors point out that past research in girls' soccer suggested the bigger ratio between the size of the ball and girls' necks, compared to boys' necks, might explain girls' greater likelihood of concussion when heading a soccer ball. More research is needed to explore this question further, Kerr's team writes.
In the current study, concussions were repeat injuries in just 3 percent of cases, and these recurrences were most common in girls' field hockey, followed by football and girls' lacrosse.
The most common symptoms to look for were headache, dizziness, difficulty concentrating, and sensitivity to light or noise.
Most of these symptoms were gone within two weeks, but almost one in four athletes required more than 28 days to return to play.
"I think the most interesting finding is not related with the data itself, but rather the comparisons that can be made with other concussion surveillance research," Kerr said.
"There is typically the assumption that higher level of competition yields a higher level of intensity, which may be associated with a greater risk of injury," he said. "However, we found high school sports in which concussion rates were higher than those reported at the collegiate level . . . in certain sports and settings, such as football and boys' soccer.
"We as the public need to use research findings to help push for concussion prevention strategies that will benefit our young athletes," Kerr said.
"These can range from programs that push for better tackling and blocking strategies or policy that reduces or restricts potential contact among players," he said. "The research should serve as a starting point to engage in a dialogue on how to protect the health, safety and wellbeing of our athletes."