Good. I'm glad to see there is a recognition that this is an important topic and that people do want to discuss it. And there are some persuasive points to be made on both sides of the argument. I'm going to start - re-start - the ball rolling by linking to the wikipedia article on the subject. Wikipedia is not an authoritative source, but this is a useful article that covers a fair bit of the ground and contains links to sources that are authoritative.

And I should also re-state my own position. I own one of the more expensive models of cycling helmet. I never wear it unless I am taking part in an event in which helmets are mandatory. I do not race, I do not do stunts, I am not a downhill mountainbiker (in fact I am rarely any sort of mountainbiker) and in my judgement, the risks I run while cycling are so small that a helmet - irrespective of its effectiveness - is not necessary.

Those who promote helmets say this is foolish, that accidents can happen anywhere, that I should wear a helmet as a precaution. Leaving aside the question of whether helmets are effective, this is a reasonable point. However, it would be no less reasonable were it asked of pedestrians, or of those walking down stairs in their home or office building. In the UK the number of fatalities among cyclists per mile travelled is about the same as it is for pedestrians. I ride much further than I walk, so I am more likely to get killed while cycling than walking. But this does not mean that cycling is more dangerous than walking - they are equally dangerous, it's just I do more of one than the other. And it never occurs to me to carry a helmet so that I can don it while crossing the street, so why should I worry about it when just riding along? And even though I cycle a great deal, my odds are still excellent. Again in the UK, which is where I live, there is only one cyclist fatality per two million miles of cycling.

This is at the heart of my disagreement with those who insist on helmet use. Their message is that cycling is inherently dangerous, and should be practised only when wearing protective gear. Cycling is no more inherently dangerous than other everyday activities, and much more beneficial than most. The referenced wikipedia article contains a link to a British Medical Association article that estimates the health benefits of cycling to outweigh the risks by 20:1. Yet the message we send about it is that it is dangerous and if you do it you might die. This discourages cycling, and this really does make it more dangerous for those cyclists that remain. In those parts of the world where cyclists are very numerous, injury rates per mile travelled tend to be lower. In the Netherlands, where cyclists are everywhere and almost nobody wears a helmet, cyclists suffer fewer head injuries than in the US or UK, for example.

Cycling is good for you. If you exercise reasonable care and learn how to ride a bike in traffic, you are unlikely to come to any harm, with or without a helmet. If you wish to wear a helmet that is fine, but it would be sensible to ask yourself what you expect from it. If it is to spare you some superficial damage in the unlikely event that you fall off and the still more unlikely event that in doing so you hit your head, go to it. If you expect it to offer meaningful protection in the event that you are hit by a fast-moving motor vehicle, you're likely to be disappointed.