Advocacy & Safety - when is it time for a new helmet?

i have a helmet that i've used for a few years on all my trail and road rides. it's never taked a fall, most trauma it's ever seen is probably getting tossed into the back of my van.

my question is, does a helmet "go bad?" or is it pretty much safe until i crack it or wear out the straps or something?

My helmet has an instruction saying to replace after three years (Bell metro) because of changes in the composition in the foam inner.

It's definitely time to replace a helmet when the pads and straps start to rot.

UV rays will degrade the foam in a helmet reducing its effectiveness. Every 4-5 years has always been my rule of thumb, but I'm at 52 degreess north where the UV index rarely crests 8 its probably a shorter time period where you are.

I replace mine every two years or so just to get something new. I have one that's sitting in the garage after two years of use and it appears to be fine. Around here, the sun bleaches and discolors. I suppose that might also be a reflection of an earlier poster's concern about breakdown in the foam. I don't think I'll ever wear a helmet longer than 3 years. Then again, I only spend $40 - 50 on 'em. Some spend a couple hundred. Not at al sure I'd want to replace a very expensive helmet at all.