Anyone selling helmets tells us not to use them after they are x years old (I forget what the time limit is supposed to be), but I have never heard this from any source that wasn't trying to sell me a helmet. I checked on the Snell and DOT sites, but didn't find anything on aging.I very rarely have passengers and have a couple older, hardly used helmets. So, if a helmet isn't dropped, and isn't stored in UV light, how old is too old?
I guess it depends how old an "older" helmet is...
The date of manufacture has been marked on helmets since the mid-80's (1984, I think). If your helmet has no date, then I'd definitely toss it.
The MSF folks say replace every 2-5 years IIRC, and that seems to be based on guidance from the manufacturers AND Snell.
Here's a quote from the Snell website:
"Why should you replace your helmet every five years?
The five year replacement recommendation is based on a consensus by both the helmet manufacturers and the Snell Foundation. Glues, resins and other materials used in helmet production over can affect liner materials. Hair oils, body fluids and cosmetics, as well as normal "wear and tear" all contribute to helmet degradation. Petroleum based products present in cleaners, paints, fuels and other commonly encountered materials may also degrade materials used in many helmets possibly degrading performance. Additionally, experience indicates there will be a noticeable improvement in the protective characteristic of helmets over a five year period due to advances in materials, designs, production methods and the standards. Thus, the recommendation for five year helmet replacement is a judgment call stemming from a prudent safety philosophy."
A polycarbonate-shelled helmet that hasn't been used much and is not exposed to UV, chemicals or anything else noxious should be good for 5 yrs. Essentially, what I gather from the Snell statement is that they aren't saying that the things are useless after 5 years, just that it makes good safety sense to change them that often.
The problem is that there are so many variables in play and no way to know from a visual inspection if the helmet safety is compromised. I'd err on the side of being very conservative and tossing an old(er) helmet - the passenger's safety is MY responsibility.
Dunno if this helps or not...