One of the major distractions of motorcycle touring is that, after the first couple of hours, the hair on my forehead begins to itch and there is a nagging desire to stop, take off my helmet, and scratch. I guess its the being bent backwards at the roots or the motion of the helmet relative to my head over time.
I also know that its the shape of my helmet. My old HJC was a little tight in the forehead and I'm sure the extra pressure didn't help the blood circulation. The new Shoei is a little better, but I still had itch in the Shoei after a time.
This weekend, I may have come across a potential cure. I have been travelling for more than 6 weeks now and my last haircut was last year. This is the longest my hair has been since long hair was fashionable in the 70's. So last weekend, using my old HJC helmet (thank you, John), I rode for 5 hours with occasional stops. The long hair folded straight down into my face and, amazingly, no itch.
Now others have done the shaved head thing and I suppose that would work too, but I'm not ready for that.
August, 2011 Update
I don't usually pass on commercial interest comments, but the comment on M-Gen is interesting. Looks like a scientific approach to the problem of helmet itch. I haven't tried it. It's kind of pricey and has to be shipped from England, but it is interesting enough to pass along.