The Snell Foundation, a non-profit organization devoted to improving the effectiveness of auto racing helmets, recommends that, in the absence of any crashes, you change your helmet every five years. This is because the materials inside the helmet, like glues and resins, tend to degrade over time in a way that affects the liner material. Also, oil from your hair, sweat, and cosmetics all are known to cause wear and tear to the inside of the helmet, making it a less effective protector of your brain in a motorcycle crash.
If you are involved in a motorcycle accident and your helmet is impacted, you want to purchase a new one before your next ride. The protective material inside your helmet does not “bounce back” and provide protection a second time around.