Bike bike helmet smells like daisies in comparison to my riding (horse) helmet (for you horse people it is a Charles Owen jockey helmet...I jump horses off cliffs so I go for the heavy duty stuff)...at least the bike helmet has vents that are useful, my riding helmet not so much. Plus, it sits amongst my saddle pads, leather, and gross gloves when not in use. It is not submersible.

SO, I use a dryer sheet to keep it fresh. I stick one in there after I ride and let it sit. It may not kill any germs (don't want to think about it) but it keeps the smell in check. I keep one in my bike bag as well and my helmet stays much nicer between washings. I do wash my helmet, but it would seriously decrease the life of the pads and such to do it as often as it probably SHOULD be done, but my hair is much happier if I keep a bounce sheet in there with it.

Having said that, I do not have sensitive skin. My husband's delicate skin would never survive.