As a former bicycle racer, I strongly advocate helmet use. Having been in many frightening crashes, I can firmly state that I wouldn't be here if I hadn't worn one all those years ago, OR maybe I would still be here, but in a greatly reduced mental capacity. (I know, you're all saying how much lower can I go anyway!) I cracked many of them and banged plenty of others hard enough to be unsure of their future effectiveness. Rather than take a chance, I would just buy a new one.
That may no longer be necessary in the near future. Developers at the Fraunhofer Institute for Mechanics of Materials in Freiburg have added a layer of microencapsulated oils which stink when released. This could be quite effective as long as the oils don't smell anything like sweat. Heavily used helmets already have a "bouquet" from all the sweat absorbed in the helmet's cushioning pads. And maybe some of the energy drink that you poured over your head thinking that it was your water bottle.