If we take a closer look at the article we see that both the experiment and the control groups studied are those who have already been hospitalized for bike injuries. If one were to examine the medical and epidemiological literature on bike helmet effectiveness, you'll find the exact same condition over and over: Studies show that helmeted cyclists who are hospitalized are far less likely to have serious head trauma than bare-headed cyclists that have been hospitalized.
But wouldn't this be true, regardless of the activity? Logically, helmeted drivers should also receive significantly fewer head injuries than bare-headed drivers. Similarly, helmeted pedestrians should be less likely to receive serious head trauma than bare-headed ones.
This doesn't mean that biking without a helmet is safer than driving without one. Rather, it helps to explain why there is no comparable fear of driving (or walking) without a helmet.
How bike helmets may be harmful
But say you are someone who is concerned enough about head injury to wear a helmet while you're driving or while walking down the street. Is there an argument that says that wearing a helmet actually increases risk of injury?
Turns out that there is. There is some evidence that wearing a helmet may directly increase your chance of getting injured in the first place. In 2001, an article in the New York Times reported that the rate of bicycle head injuries had risen sharply — an increase of 51% — during a ten-year period when bicycle helmet use became widespread. This during a time when statistics showed an overall decrease in bicycling in the United States. No one knows for sure why head injuries among cyclists increased, but there are a few theories.
First, wearing a helmet changes how drivers perceive the cyclist. A University of Bath study showed that drivers, when overtaking cyclists, gave helmeted cyclists significantly less space than they gave cyclists who don't wear head protection. The study found that drivers were twice as likely to pass closely to a helmeted cyclist, and that drivers passed an average of 8.5 cm (3 1/3 inches) closer when the researcher was helmeted than when he was not. Not only does this increase the chance of being clipped by a vehicle, it leaves cyclists with far less maneuvering room to avoid other potentially injurious road hazards like potholes and icy patches.
Second, the design of the helmets themselves may increase the chance of some types of injuries when incidents do occur. Three separate studies have shown that bike helmets may increase the probability of certain types of neck injuries. There's some evidence that having an enlarged piece of plastic and foam on your head increases the probability of hitting an object that you'd be able to avoid in the first place, or that otherwise glancing contact with a surface becomes a full-on blow when the head is helmeted.
Finally, wearing a helmet may create a false sense of security and induce risk-taking that cyclists without head protection might not make. Those wearing helmets may take risks that they wouldn't otherwise take without head protection.
There are even some startling statistics that show helmets may have little to negative effects on the incidence of head injuries outside of the cycling world as well. A recent study from the National Ski Areas Association found that, despite a tripling of helmet use among skiers and snowboarders in the United States since 2003, there has been no reduction in the number of snow-sport related fatalities or brain injuries. On the contrary, and 2012 study at the Western Michigan University School of Medicine found an increase in head injuries between 2004 and 2010 despite an increase in helmet use, while a 2013 University of Washington study concluded that snow-sports related head injuries among youths and adolescents increased 250 percent from 1996-2010, a timeframe that also coincides with the increased use of head protection.
Helmets = fewer cyclists = more danger
So as much as helmets decrease the chance of head injury when you get into an accident, they may actually increase your chance of getting into an injury in the first place.
There is another significant way that the use of helmets harm cyclists: Bike helmets discourage cycling. An Australian study on mandatory helmet laws concluded that laws that required cyclists to wear head protection actually decreased the number of cyclists on the road. The implication of this study? The fewer cyclists on the road, the less likely drivers will be accustomed to sharing road space with cyclists, ultimately increasing the hazards faced by cyclists and further dissuading people from hopping on their bikes.
As an environmentalist, this is very troubling. To improve public health and the environment, we need to do the exact opposite. People should be encouraged to take a quick bike ride, not the other way around. Unfortunately our society has conditioned cyclists to feel unsafe without a helmet, even though wearing one might actually increase the chance of a collision with a vehicle; and even though other activities capable of inflicting serious head wounds are enjoyed bare-headed without stigma.
The ultimate way to make cycling safe is to promote a culture of cycling, not bike helmet use. Helmet use is very uncommon in bike-friendly cities like Copenhagen and Amsterdam, where cyclists have been socialized to see cycling as a safe activity. In order to promote the same culture here, we need to encourage people who don't bike that they should give it a try. If biking without a helmet can help with that, then great. Especially since it's not conclusive that cycling with a helmet reduces your chance of getting injured.
If there was conclusive proof that bike helmets reduce the total number of serious head injuries compared to other normal activities, then I'd reconsider my stance. But if I'm not the kind of person who wears a helmet when I take a walk or get behind the wheel of a car, then there's no logic to me wearing one when I'm on a bike, particularly if I'm confident in my urban bike safety ability.
Meanwhile the proof is pretty strong that vehicles give me more space when I'm biking without a helmet. In a city biking, that's the kind of injury I'm most concerned about. And I want to encourage more people to get on their bicycles, because the more cyclists out on the road, the safer I'll be.
... it is hard to overstate how our unnatural obsession with head protection is stifling the growth of our bicycle culture. It achieves little, except deterring the most casual cyclists, who also happen to be the slowest and safest ones on the road