A:Excellent question. As someone who has twice dodged severe head injuries because of my diligent wear of a bicycle helmet, I’m pretty sensitive to this topic.
And you raise the exact point—what effect does sweat and the sun have on a helmet? And the answer is this: Quite a bit. Sweat and the salts it releases are acidic and corrosive, even eating away at plastic. And the sun is simply brutal on plastics, which is why any pack you wear for a few summers will start to fade (and the fabric greatly weaken).
So what to do? You can take a few steps to prolong the life of a helmet. Every other week or so, dunk it in a bucket of cool water and swish it around some. That will help clean out dried sweat. And of course, try to store it out of the sun, someplace dry and cool.
Otherwise, I really recommend getting a new helmet every other year or so, if you’re a real consistent rider. Otherwise, every four years. I mean, why take the chance? Even if it looks fine, it will have been weakened by the elements. And of course, any helmet that has suffered an impact should immediately be taken out of rotation. After all, a decent helmet is exceedingly cheap insurance—under $100, unless you really want the latest and sleekest.
If you are due for a new lid, these are my picks for the best, most affordable helmets out there for every biking style.