Soundbytes

• 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.
• So: cycling is not dangerous.
  
• Cycling causes head injuries!
• Cyclists have about the same proportion of head inury as pedestrians, something which is stable over time.  There is no credible evidence that cycling is unusually productive of head injury.
  
• So: Cycling is not a special risk for head inury
  
• 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 thedread 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.
• So: 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.  Except that this figure is an outlier, a single study well in excess of the figures in any other study, and when the authors reworked the data in 1996 they came up with a much lower figure.  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.
  
• So: the number 85%/88% is a lie.
• And prevents x% of head injuries is also a lie.
  
• 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 helemt 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 propoinents will likely increase the perceived protection that helemted riders feel, meaning they take even more risks.  Read the Munich taxi experiment for more on this.
  
• So: There is a downside.
• If you don't wear a helmet you have nothing to protect!
• 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?