Originally Posted by
Brian Ratliff
Helmets don't lose the ability to absorb energy, unless exposed to extreme conditions. Since shells started to be in-molded, there is no harm from minor impacts. It used to be the little foam pellets were the only things keeping the helmet's shape and if it were cracked it would risk falling apart. Not anymore.
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The Snell Foundation thinks that they do break down over time, and recommends replacement every 5 years.
http://www.smf.org/helmetfaq#aWhyReplace
No idea how much data they have to back that up, but it seems like a reasonable time frame.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.