I ALWAYS wear a helmet. I have ALWAYS ALWAYS worn a helmet. My mother got a head injury once standing over her bike without a helmet when a dog ran into her, and she toppled over on her head. My whole family suffered for years from her injury. She was not, however, in motion at the time.
It's true that wearing a helmet flattens your hair. It also can look dorky. On the other hand, I once knew this really cool guy who wore his helmet all the time. We were sitting at a cafe for hours, and he never took it off. That said, I was compelled by this research that scientifically proves that helmets do NOT make you safer.
From Velo Mondial:
The active promotion of helmet use by cyclists is a fiercely controversial and often emotional subject, with views put forward with great conviction both for helmets and sceptical of their value. Controversy is particularly acute with regard to mandatory helmet laws. But the heart of the matter is: Less cycling increases risk for those who do cycle: Safety comes in numbers! It is also logic to wear a helmet if you are a child or a speed cyclist. Helmets do not help when in collision with cars; the difference in speed between car and cyclist or pedestrian cannot be compensated by a helmet. Helmets can even suggest to car drivers that the cyclists are safe. Then they are better off without. Read more at the Bicycle Helmet Research Foundation.