Bike helmets are designed with the expectation that they are going to become sweaty, salt encrusted, and be exposed to water, as in rain for example. If your helmet straps are getting too gross for you, then simply rinse the helmet in its entirety in the kitchen sink or someplace similar and let it air dry. IT WILL NOT HURT THE HELMET. All the rest of this discussion with regards to special detergents, Lysol, shampoo, or whatever, is - with all due respect - ridiculous.