The manufacturers now say three years from first wearing on some of the newer helmets, and that makes sense to me, with the increased surface area of lightweight helmets. The surfaces are what get exposed to body acids and oils, UV light, ozone, and all the other things that degrade EPS.

Neither Snell nor BHSI has revised the five-year rule that has been the recommendation since before they even had websites.

Do be aware that the clock starts from first wearing, not from manufacture, assuming a helmet has been kept in the box, not displayed in the sun and not tried on excessively. If you're buying a hat that's obviously been on the LBS shelves for a while, I probably would go from the manufacture date (and try to negotiate a discount accordingly).

So between those two ... I don't know that anyone here has the expertise to really say. I'm with TriGirl, it's my head, I've landed on it or near it enough times to not mess with it. I don't start panicking when three years have gone by, but somewhere between three and four years I'll replace it (assuming I haven't landed on it sooner ).