You strike a real point on human sweat. I work part time at a friend's bicycle shop since retiring. We see the rider's sweat actually eating into bicycle frame carbon joints, rusting steel frames, and etching aluminum frames. We see it eat cables and even break down the front hub bearings on occasion. Human sweat is way more caustic than most people know. This is why it adds fuel to the debate about the 3 year life span of a helmet because of its ability to damage the inner impact absorbing material.

 

I guess for all you guys who live in humid climates, sweat would probably be a big factor...

 

What I've experienced is that I get about 3 to 5 years out of helmet. The liners compress and break down for all the various reasons previously mentioned. The helmet just does not fit as good as it used to and subjectively loses its protective qualities. I recently upgraded to a new helmet and could not believe the comparison with the old one. It felt like a fish bowl flopping around (the old helmet)!

To answer your question about what to wash it in. I use the kitchen sink, warm water and shampoo. Gently wash the liner/helmet, rinse out the soapy brown water until clear, and let it drip dry for a day. The helmet smells good for a while too! Naturally its your helmet and you gotta go with what you are comfortable with concerning the wash process.