Personally I don't use a helmet, don't even own one.
There was a time I road a motor cycle with out one at much higher speeds than any bicycle could ever hope to achieve.
In my younger days when I had hair a bandanna as about it, it kept my long red locks from getting tangled.
When I was a kid I pulled off some pretty risky (Do Not Try this At Home) crap to and earned some big lumps.