I wear a cycling cap and wash that more often. I probably should wash my helmet more often and if I did I would probably use my normal Dr. Bronners and cool water or shampoo it in the shower. As far as replacement every 3-5 years works fine for me, I know some people are cheap with safety and want to say it's fine but with use and element and temperature exposure I see no reason to take the risk. Certainly yet is does suck especially when I have found a taste for higher end helmets but I can get a cheap one if need be for $40 and I will be fine. $40 every 5 years isn't a bad deal and even $100+ isn't that bad. You could probably put your spare change in a jar for that amount of time and get yourself a nice Lazer X1 or Giro Synthe (or the new one) or a Kask Protone or whatever every 5 years easy.