Dermarolling will not damage healthy skin. The "secret" of dermarolling and many other rejuvenating methods such as certain laser treatments is to cause some very mild damage to the skin. It is a trick to make the body repair the damaged skin. The skin gets rejuvenated as a side effect of this repair. The damage has to be substantial enough to induce repair but not too serious to cause scarring.
The holes made by a dermaroller are miniscule. It is a misunderstanding that with 0.25 mm diameter needles, that the holes will also be that wide. The skin closes itself around the pricks immediately. The outermost layer of the skin is not removed by dermarolling (contrary to ablative lasers or deep peels) and there is a lot of intact skin between the microholes made by a dermaroller. This promotes very rapid healing.
Those methods where temporary skin injuries are caused by heating up the skin tissue are much more prone to potential burns and scarring than dermarolling where the injury is caused mechanically.
The body will never restructure the skin "for the worse" unless the damage is so great that the injury will become a scar. When you accidentally prick yourself by a sewing needle, it will heal without a scar. If you cut yourself badly and deeply by a knife, it may become a scar. Larger injuries become scars, smaller ones don't. There is no intermediate stage. Either a scar for larger injuries, or nice new skin for micro-injuries.
We recommend targeted needling with our custom made single needles for individual scars (except for keloids) or wrinkles. Single-needling is done more densely and deeply than dermarolling. It crushes the hardened collagen bundles and induces new collagen. Nothing can go wrong, because you're already pricking an ugly scar. Instead, the skin is persuaded to replace it slowly with more normal skin, by making micro-injuries into the scar. A micro-injury is repaired by normal skin, so the tiny pricks into the scar will turn into normal skin. Hence the need for intensive, dense pricking there and less agressive pricking on less scarred, more normal skin. You can see a result of single needling here:http://forums.owndoc.com/dermarolling-microneedling/Does-dermarolling-work-for-surgery-scars