I started out 1.5mm, but now I’m concerned about scar tissue. I’ve heard 0.6mm might be better, but the redness goes away pretty fast. I started out doing once-a-week needling, but then I’ve seen people who did it twice a week at a lower depth followed by minoxidil that had great results
Microneedling depth should be able to reach the stem cells at the top of the hair follicles which lie about 1mm below the skin so 1 of 1.5 mm microneedles are about right. These stem cells have some cells that specialize in hair cycling so that when stimulated, the command goes out to the other stem cells to kick in the anagen cycle (theory at present).