Wear a helmet on your knee...
...since your knee will get it first. In fact in my 20 full time seasons over the last 35 years, I don't have an event that would have needed a helmet...except perhaps... the turkey in the lift line imitating a helicopter. I have cut my forehead on my ski-pole grip and cut my lip sliding into a gate and done my ankle slipping on ice in my ski boots and ankle and shoulder and knee etc. but so what? The only reason for normal skiers to wear helmets is to be fashionable and to have someplace to crank the tunes...and I'm sure the hearing-sense is worth more than imagination.
The other thing that is not part of MY imagination are the poor impact standards in helmets used in skiing check out this:
http://www.clydesoles.com/Front/Helmets.html
If you don't think much of this dittie- search for studies of soccer players having short attention spans and memory problems from merely heading the ball ( and, to be fair - running into each other and goal posts.)
Minor concussions, like heading also lead to the anger management problems often found in park-rats and skaters who have had their bells rung too often. A helmet won't protect from brain-slosh injuries which occur far more frequently than impacts which would be protected by a helmet.( i think these lesser injuries are called scalping)
Again - how frequent are head injuries 'requiring' helmets and the injuries actually prevented by helmets.
And then I found this page
http://jama.ama-assn.org/cgi/content/abstract/295/8/919
But I still ain't gonna wear a bucket.