I'd always assumed that bike helmets were a safety no-brainer (so to speak) like seat belts, but according to this (extensively footnoted) wikipedia article, the evidence in their favor is sketchy at best. It's probably still a good idea to wear one, but... - ⓞnor

Very interesting. I had no idea that the evidence was so weak. - Paul Buchheit

I never wear one, but wouldn't drive an inch without my seat belt on. - Anthony Citrano

You guys might not remember the time I got Boeri to offer all Googlers massive discounts on ski helmets before the annual trip to Tahoe. I sent out a note to Misc excited to be sharing this with the company. Over the next hour, I was crucified for being such a naive jerk as to assume that there was any data that a helmet could save lives, etc. Classic Misc. :) That said, anecdotally, I have had my life undoubtedly saved by both a ski helmet (probably twice) and a road bike helmet. - Christopher Sacca

My cousin, an experienced cyclist, recently was in a bad accident including broken neck vertebrae. There is little doubt that he would have been paralyzed or worse without a helmet. Maybe I've just been programmed, but I find it hard to believe that it would be harmful, or non-helpful, considering the copious evidence there is about the efficacy of motorcycle helmets. (Or is that specious as well?) - Kevin Fox

Kirk: Interestingly, the wikipedia page says that modern bike helmets are poor at protecting the back of the head, and people who engage in stunt cycling should probably use a different helmet. Glad it worked for you, of course. Kevin: Motorcycle helmet use does indeed seem to be well supported by statistics, partially because motorcyclists are more likely to hit their head hard, and partially because motorcycle helmets are much more protective than bike helmets. - ⓞnor

"The major causes of permanent intellectual disablement and death after head injury may be torsional forces leading to diffuse axonal injury (DAI), a form of injury which usual helmets cannot mitigate and may make worse.[61] Helmets may increase the torsional forces by increasing the distance from the centre of the spine to the outside of the helmet, compared to the distance to the scalp without a helmet." - Paul Buchheit

There must be one VERY dedicate person behind most of that wikipedia page. - Nicķ

It seems unlikely they're directly harmful; the rotational force argument seems weak to me. The indirect harm mostly happens by discouraging people from cycling, or by giving people a false sense of security. My take-away is that I should wear a helmet, but avoid trusting it to protect me, don't support mandatory helmet laws, and don't be judgmental about other people who don't wear them. - ⓞnor

"In real accidents, while broken helmets are common, it is extremely unusual to see any helmet that has compressed foam and thus may have performed as intended." - bob

If nothing else, this makes we wonder whether bike helmets are poorly designed. I'll keep wearing mine, but it's a little disturbing that they can't show better evidence of efficacy. - Paul Buchheit

@Nick: I'm guessing *two* very dedicated people who both respect the spirit of Wikipedia a great deal. - Kevin Fox

torsion: actually, why doesn't that make sense? The longer the lever, the greater the force. - j1m

It's just hard to imagine that's a bigger effect than the protection a helmet grants. - ⓞnor

maybe it lessens external injuries like scalp damage, skull fracture, etc but increases internal ones - ""The major discovery is that the skull plays an important role in protecting against rotational acceleration," says Phillips. He says almost all head injuries involve not just a direct blow to the skull but also damage to blood vessels caused by the brain rotating within the skull. In mechanical terms, the head is an elliptical spheroid with a single universal joint, the neck. It is therefore almost impossible to hit it without causing it to rotate. The head tries to dampen these forces using a combination of built-in defences: the scalp, the hard skull and the cerebrospinal fluid beneath it. During an impact, the scalp acts as rotational shock absorber by both compressing and sliding over the skull. This absorbs energy from the impact." " - bob

I managed to read a bit, until I got to "Ordinary cycling is not demonstrably more dangerous than walking or driving, yet no country promotes helmets for either of these modes." At this point, having noticed I was reading the writings of a fool, I moved on. Not that that's not good snark. - j1m

Read the discussion page & history. A couple of people who are convinced that their view is correct, and a whole lot of people going WTF?! - Nick Lothian

I was just discussing this with my wife. We decided that there's no point in requiring our children to wear bike helmets because it's so unlikely that they would get into an accident where a helmet would actually save them. - Gabe

Is that because they don't exist Gabe? - Paul Buchheit

Sadly, the community we live in requires bicyle helmets for kids under...12? 14? Irritating. I mean, I understand what they're trying to do, but still. - abacab

I never wore a helmet while biking pretty much every single day in Europe for 25 years, but after I moved to America, I kept getting dirty looks from other bikers, so I decided to bow to peer pressure and wear a helmet... - Frederic

Paul: Since we're working on having kids, we frequently have discussions about how to raise them. - Gabe

Once in high school I forgot to tighten the quick release for my front wheel. Wheel came off when I went off a curb and the helmet saved my face and head from serious damage, although I still suffered a concussion. Based on that single experience, I think you are better off wearing it than not, but that's just me. - Scoble, Alex Scoble

Well, one claim is that lots of people assume that the helmet helped them in an accident when it might not have (other than by preventing superficial skin cuts). Hard to say. - ⓞnor

I like to think that when I wear my helmet I'm more careful because I'm acknowledging that I'm engaged in a dangerous activity. - Kevin Fox

@Gabe. I hope you're having fun working on making kids :) What do you think about other safety precautions like gates in front of stairs and special electrical outlets. I think it might be good to let our children know that the world is a dangerous place, instead of trying to create an artificially safe world for them at home. - Robert Felty

Rob: I'm not concerned about electrical outlets. I've gotten enough 110V jolts to believe that it isn't dangerous enough to seriously hurt them, but will teach them not to poke stuff into walls. I thought gates are used to keep them out of places I don't want them, not for safety. - Gabe

I've read that cars drive closer to bicyclists with helmets than without, which would increase the risk associated with biking while wearing a helmet. - Melinda Owens

Melinda: that was the case in two UK towns, Salisbury and Bristol. personally, I doubt that result would translate outside of the UK -- it's going to be very specific for that locale's driving culture. Personally, I don't even think it translates to where I cycle, in Dublin, Ireland - Justin Mason

@Frederic, that the US for you. @Robert, "that's why I let my kids use chainsaws..." - j1m