It's either what @CoriM mentioned or it's what I assume is a natural shedding of the very top layer. I noticed this on my drakes often but I don't remember if I've ever noticed my hens like this. My Pekin drake has this now and he's just finished his annual molt. I have always thought it was related. One of my Call drakes has this and he is beginning to molt. I don't ever do anything for it, but I know it's best to not pick at it, just in case it gets deep at any area. I'm outside now locking everyone up. If I can get pictures of my drakes that look similar, I'll share them here later tonight. Lockup usually takes me a while.