i dont see how u can scar or burn ur skin from probing the needle into ur skin if that is the case then no matter even if u insert without it turned on ur,ll get damage and in any case the power suply is nearer ur skin when u insert into hair which would more likely burn rather than the tip when turned on the current goes throughout the needle not just the tip and more so at the base
You are not inserting the needle into the skin, you are slipping it into an existing hole called a pore. As long as you follow the pore and don’t insert deeper than the pore, you would not do any damage.
When you apply current, there may be more moisture at the base of the pore which would conduct current better than the surface. Even without insulated needles, my experience has been to see reactions occuring deeper in the pore and pretty much no burning at the surface. It’s not so much what is closer to the power supply, but what can conduct better. Using insulated needles can help eliminate current flowing from the probe shaft.