I used a 1mm dermaroller for a couple of years and it never did any damage though I am also not sure it didn't anything very beneficial. I recently bought a 2mm one thinking it was perhaps more effective and I tried it yesterday. I am writing this to warn anyone else from doing this at home. I used the roller on one area on my leg and after an hour I realised I had severely injured my skin with marks and mild bleeding. I am mentally prepared to have permanent scarring from this. Girls don't do it.