Helmet degradation

i think it all depends how often you ride,they recommend changing every 5 years,but if you are only using it a few days every week compared to say a courier who would be wearing it every day, i would say you could easily double that life span.It's the sweat that degrades it seemingly, so if you wear a silk balaclava or similar under your lid you would think it would last even longer.

 

I think this is a good read:

http://www.eagleleather.com/Helmet-Fact-vs.-Ficion:-How-Often-to-Replace?-643/