I don't wear a helmet because I don't like them and don't think even at best they offer any significant protection. But beyond this simple gut personal preference, there are three factors that convince me that wearing a helmet - for the kind of cycling I do - would be a positively bad thing to do.
The first is my personal experience, drawn from two proper 'at-speed' crashes, that in the event of any such, I instinctively compose my body in such a way as to protect my head - and that a helmet, simply by reason of its bulk & shape, would make it more difficult for this to happen. In both of my crashes, everything happened so fast that I can't claim any recollection of exactly how this is achieved, but it feels intuitively likely - the body has a great instinct for self-preservation in a crisis, and has extensive form in prioritising protection of the most important bits - and it also tallies with my experience: in both incidents, I emerged bleeding copiously from multiple wounds, but my head was pristine, not so much as a bump.
The second is evidence that helmets can snag in the event of impact, turning what would have been a nasty graze into neck-snapping whiplash. I have to admit I view these with a certain wry scepticism. No doubt it can happen, but I'm doubtful that it happens very much. Nevertheless, I'd rather take my chances with any amount of scrapery than risk even the slightest chance of a broken neck.
The third and to me the most compelling is the extensive evidence that drivers treat cyclists differently when they wear helmets. They pass closer, and at greater speed. And as an urban cyclist, the behaviour of drivers is by far and away the biggest single factor in deciding my chances of survival. My theory runs as follows: the moment you put on a helmet, you become, in a certain kind of driver's eye, 'a cyclist' (and such people, to paraphrase the great Malcolm Tucker, farking hate farking cyclists), and thus fair game for all sorts of treatment even such people wouldn't inflict on other 'people', who even they recognise as being in at least some sense, like them. To put it at its simplest, a helmet turns an 'us' situation into an us and them situation, and that's when things go pear-shaped.
Personally, then, I prefer not to wear a helmet. I prefer riding without one. There's significant evidence out there to show that I'm at less risk of any kind of incident when not wearing one. And there's also significant evidence - both third party and personal/anecdotal - to suggest that the consequences of any incident are less likely to be severe/life-threatening without one.
I have - let me stress - absolutely no beef with anyone choosing to wear one. NB also my very first caveat - "for the kind of cycling I do" - others' experience may differ. But I take serious issue with any talk of complusion. I take great umbrage at, eg, the BMA's endorsement of helmets/compulsion. And I get very angry when I hear of ignorance in authority: from nurses tutting victims to judges apportioning blame to insurers reducing payouts. Hopefully if ever I find myself encountering any such I will have enough of my wits left to enlighten them with the contents of this post...
