Replace Your Helmet After One Impact
There's no challenging the fact that helmets are essential to cycling safely. Studies indicate that helmets may reduce the risk of bicycle-related head injury by as much 85%.
But as protective as they are, bike helmets are not indestructible. They are considered "single-impact" gear: After one fall or crash where you hit your head, you should discard the helmet and get a new one. Even if there are no visible dents or damage, you should replace the helmet; minor impacts alone can affect a helmet's ability to protect you.