Pyloric Stenosis is an interesting and well understood condition. It affects boys much more than girls. In fact, it often affects the first born males almost 4 times more than others.
Hair cells, divide so often, that they can duplicate themselves in a few short hours. Some divide faster, that is why some hair grows quicker. As we get older, the cell division, for the most part, slows down. Only the cells of bone marrow grow quicker. Pigment changes results in hair color graying.