Hi there,
I had this conversation with a friend of mine who is a long time serving flight crew member.
He said that the hats had been taken out of the uniform in some companies due to a hairloss worry!
Don't know if theres any research on the matter, but it seems that when it gets warm problems with the scalp can occur if under a hat all day.
Though I must say, I feel they added an extra zest to the uniform especially the Captain's with the fried egg on top!
WB