The modern bicycle helmet can withstand astonishing forces, but because it must be lightweight to be practical, it’s also more fragile than it first appears.

Now that good riding weather has finally arrived, here are tips for helmet care that will keep your helmet working at its best—and help you figure out when it's time to buy a new one. (Check out our updated bicycle helmet ratings here.)

Do store it properly: According to Ian Hall, an engineer with the Consumer Product Safety Commission, helmets should be stored away from extreme heat, which means that keeping it in the trunk of your car is a bad idea. The temperature inside a trunk can prevent a helmet from adequately absorbing impact. Store your helmet in a cool, dry place.

Don't expose it to chemicals: The foam and the plastic shell on a helmet can be damaged by certain cleaners. Cleaning a helmet with harsh chemicals, such as ammonia or bleach, and even decorating it with paint, can potentially degrade the materials and possibly its performance.

Do replace it after a crash: This is a helmet care must. Your helmet is designed to withstand a single impact. One. That’s it. After you’ve been in a crash, buying a new helmet and trashing the old one is mandatory.

“Damage can sometimes be hard to detect,” says Hall. “The liner compresses on impact and loses the ability to absorb additional energy.” Helmets more than five years old are also candidates for replacement. Some manufacturers even recommend replacing your helmet earlier than that.

Don't accessorize it: Think twice before mounting an action camera on your helmet. The strap and/or adhesive mounts could damage the helmet, especially if they’re installed less than perfectly. But the larger problem is the camera itself. A helmet is designed to have a surface without protrusions, and a camera represents a significant one.

The American Society for Standards and Materials is developing performance requirements for helmet-mounted accessories, and the CPSC is monitoring the effect of helmet-mounted cameras. “Anytime you add an external component to a helmet, you can change the performance of that helmet,” says Hall. “A helmet-mounted camera may become a projectile if it detaches in a crash, but a camera that remains attached could focus the forces applied to the rider’s head, increasing the risk of injury.”