https://www.facs.org/about-acs/statements/statement-on-bicyc...

Helmets reduce the risk of head injury by 48%, traumatic brain injury by 53%, facial injury by 23%, and fatal injury by 34%.2 Pediatric non-helmeted bikers have a 3-fold higher risk of serious head injury compared to helmeted bikers;3 one study suggests that helmet use may reduce the risk of head injury by 83%.4

Bicycle-related head injuries and deaths have decreased in states that have enacted bicycle helmet laws.5

Larger effects are found when legislation applies to all cyclists than when it applies to children only. 6