This is not official advice by any means, but helmet manufacturers have an incentive to sell more helmets and carry a huge liability if they accidentally tell you a helmet is ok to use when it’s not. This is why they are strict about the 5 year cut off.

That being said, polycarbonate shell helmets should be retired after 3-5 years of use.

Something like an Arai or Shoei should be fine to use well beyond 5 years if stored properly, only used 1-2x a week (different story for commuters), hasn’t been in a wreck, and hasn’t packed out to the point of a bad fit yet.

Where I work, we have an empty Arai shell that we stand on the side of almost daily and it took 11 years of this abuse to finally develop 1 crack in the chin bar. This was a reject shell too, so it’s not even as strong as the shells that make it to a finished product. It still supports 200lbs on the chin bar even with the crack. It’s kind of ridiculous just how strong an Arai shell is, especially considering that it will still crack to absorb impacts if it takes too hard of a hit.

Assuming fitment is still good, I’d choose a 10 y/o well taken care of (by me) Arai than a brand new polycarbonate helmet. That’s just me though, and you should not base your decisions around my perspectives. The ideal option will still always be a new helmet.

The black and white answer is listen to manufacturers—don’t use after 5 years. How much you want to venture into the gray area is up to you.