Is there any evidence for this, I mean in terms of causal evidence, to indicate how, wearing a helmet, could cause on to hit one's head more? If it's merely statistical evidence, it would merely show a correlation between helmet wearing, and accidents. (Apologies if this has been covered 50 times already, but I'm keen to know if I'm endangering my cranial health in wearing a helmet when not compelled to).
Lots of ways.....
Given that it increases the size and weight of the head, a close call becomes a strike. Secondly the added weight will cause the head to travel further with greater acceleration, increasing the impact
Then we have the problem of modern design where the vents and sharp edged can catch on obstacles or rough ground. Instead of sliding, the motion is arrested and imparted to the brain, and secondly this can cause rotation which in turn results in neck injuries as well as rotational injuries to the brain