Depending on useage you should replace your helmet every 3-5 years. I have a friend who I have been telling to replace her helmet because it looks old. She maintained that is was only a couple years. I said, yeah but you use it every day and went touring in new zealand for 6 months with it. The styrofoam is brittle from all the UV exposure. She crashed recently and it cracked into many pieces. Off road. While a new helmet might have also cracked, it would likely have cracked into fewer pieces and too more of a bruising (squishing). That is what the helmet is supposed to do, absorb impact. You should replace your helmet because it is brittle and in the event of a crash will not perform as intended. it is unfortunate that we do not have a better technology than disposable styrofoam but it is the lightest weight option that provides the most protection. Additionally, helmet fit and security seems to be improving all the time and that is reason enough to buy a new lid every three years. I have a commuter helmet and race helmet. I get a new commuter about every 2-3 years. I expect the race/road helmet (bell sweep) to last 4-5 because it is stored out of direct light and used less frequently.