Hard to refute -- I use a pretty vigorous spin-brush-dryer on my hair every day for ~5 minutes, which only does the top and front. I just noticed recently that

Hard to refute -- I use a pretty vigorous spin-brush-dryer on my hair every day for ~5 minutes, which only does the top and front. I just noticed recently that the sides have grown out beyond a few mm, and they are much grayer than the top.