When Should I Replace A Helmet?

I have had mine for 5 years now and never had an accident with it. I know they recomend replacing them in either 3 or 5 years. (depending on the manufacturer)
Loking for advice, how many people replace theirs, and if so, how old were they?

 

I replace mine about every two years, or whenever they are damaged badly or just need a replacement

 

i replace them about every three years. the latest giro i had developed a crack in the very front, don't know how it happened so it was replace with another one.

 

Mine recommends that it be replaced no later than 5 years after purchase. It is two years old and I will probably replace it sooner than 5 years just to be safe. Hopefully it is not because I needed it. I have seen studies by ANSI that state that the styrofoam breaks down to unacceptable levels within 5 years. I don't think it is like oil changes for your car, where your dealer says that you can go 7500 miles between oil changes but the guy who changes your oils says every 3000 miles.