That paper you linked to is the first research I've seen to show otherwise. I wouldn't ignore facts just because of one paper. It doesn't disprove what we know about wound healing. I read the paper, and it doesn't go against that chart at all. It says that we can wound less deeply and still upregulate collagen production and VEGF among other things while avoiding the inflammation that comes with going deeper, and this allows us to needle more frequently. I haven't really done much research on repairing skin damage, but it's certainly an interesting idea. As far as hair goes, these depths may not be enough to activate stem cells in the DP, but it would still promote VEGF. My hunch is that deep wounding once a month combined with shallow wounding daily would provide the best results. I think
@Somebody was using 1.5mm once a week and a smaller roller daily, and he had the best success I've ever seen.