I've worn the same helmet for 2 years, commuting for 9 months by motorcycle. I've never washed it.   I stuck my nose in and took a whiff... and it smelled just fine to me!

What's up?  Am I just scent-challenged?  It must stink by now, right?

maybe your cat pees in it while you sleep.  cat pee is a very potent deodorizer

Maybe since you wear it so often, you can't distinguish that particular scent anymore. What kind of shampoo are you using? Do you persperate through your head at all? And if not, are you some kind of robot? Do you have any super powers? Do you use them for good, or for awesome?

Push some new newspaper into the helmet like a liner, close the faceshield and put outside overnight on some more newspaper, preferably out of reach of animals (particularily cats). This helps get rid of old closet smell, you're not experiencing that, but maybe this will help.

Quote from: scratchclose the faceshield and put outside overnight on some more newspaper

Hm, I usually close the face shield, and set it on top of rough-sawn lumber in my garage.  Usually, my garage smells like sawdust.  Maybe that helps :dunno: .

You could put a fabric softener sheet in your helmet when your not wearing it, providing you like that smell.

I've worn my helmet and mesh gear for a year and a half (riding almost every day to work).  It's getting warm again and heading into a second summer of 100+degrees.  I don't smell any problems here either.  Must be that great flow through ventilation and all the clean air oxidizing my bodily organics.