The helmet lobby uses soundbytes as a core part of its message. This is normal in politics, though of course much less so in scientific debate. The common soundbytes are usually from the following set:

Cycling is dangerous!

Actually there is no good evidence to show that cycling is any more dangerous than being a pedestrian. US analysis shows cycling to be safer per hour than driving, and of course there is always the issue of confusing that which is dangerous with those who are vulnerable. Being a child is not dangerous, but children are vulnerable.

Ultimately the best that can be said is that cycling is about as dangerous as walking. So is cycling dangerous?

Cycling causes head injuries!

Yes and no. Cycling is not a special risk for head injury – cyclists have a rather lower proportion of head injury than pedestrians, something which is stable over time. There is no credible evidence that cycling is unusually productive of head injury.

Brain injury!

One of my biggest criticisms o the pro-helmet lobby is their deliberate use of the medical definition of brain injury, knowing that it is uniquely terrifying and at the same time not aligned with the lay understanding of the term. Brain injury, to a medic, means (obviously) any injury to the brain. Traumatic brain injury sounds terrible, but the majority of traumatic brain injuries are simply concussion. Wikipedia has a tolerably good article on concussion. I won’t belittle it, but most of us have survived concussion at some point in our lives: it is a long way from what you or I would understand from the dread term traumatic brain injury. Traumatic means caused by trauma, i.e. a blow or other incident, brain injury means injury affecting the brain, however mildly. Cycling is not a special risk for scary brain inury.

Helmets prevent 85% of head injuries! Helmets prevent 88% of brain injuries!

On my main site I call this “the biggest helmet lie“. It’s the most widely quoted figures in helmet promotion: helmets “prevent 85% of head injury and 88% of brain injury”.

To understand the many levels on which this claim is wrong you really need to read the BHRF analysis of it: A case-control study of the effectiveness of bicycle safety helmets. Suffice it to say that by the same logic helmets also “prevent” broken legs, black skin and riding on city streets.

The number 85%/88% is simply unsupportable, anyone using this figure is either ignorant or does not care about accuracy. Prevents x% of head injuries is also a unsupportable, anyone who uses that form of words is also either ignorant or does not care about accuracy. If these phrases are used, you are being sold something. Engage scepticism.

ScaryBigNumber of cyclists suffer head injury every year!

The problem with counting the number of people injured doing anything is that it tends to be presented without context. For example, the number of pedestrians killed by drivers per passenger mile is quite low, which suggests that motor traffic is not a big risk to pedestrians, but only a fifth of motor vehicle miles are on roads where pedestrians are l=present in significant numbers so the risk is at least five times what it appears to be on the face of it.

As far as I can tell, cycling is about as risky as walking. You can decide for yourself how risky that might be, but there is no logically consistent argument for cycle helmets that does not apply equally to helmets for pedestrians.

There is no downside!

Yes, there is a downside. There is a downside to helmet wearing, demonstrated many times, that helmeted riders will take more risks, something known as risk compensation. There is also a downside to helmet promotion in that it promotes the idea of cycling as a dangerous activity requiring special protective measures. Se above: cycling is not dangerous (though cyclists, like pedestrians, are vulnerable). Worst of all, the exaggerated claims made for helmets by proponents will likely increase the perceived protection that helmeted riders feel, meaning they take even more risks. Read the Munich taxi experiment for more on this.

If you don’t wear a helmet you have nothing to protect!

Apart from being an intellectually bankrupt argument, that would make the whole cyclist population of Netherlands and Denmark look like a bunch of idiots, but as it happens they are among the healthiest people in Europe. I wonder why?

Some of the smartest people I know, scientists with a lifetime’s experience of reviewing scientific evidence, are not only not helmet wearers, they are leaders in persuading others to take a more sceptical look at the evidence. And let’s not forget that any judgement based only on the opinions of A&E doctors is like a judgement on the Lottery based only on the opinions of winners…