There is more than circumstantial evidence, as posted on https://www.pubmed.com, as to the efficacy of dermarolling. In their study, they used rollers with 1.5mm needles, and essentially rolled over the entire balding area, going in many different directions. The rolling was completed once the skin was a pinkish color, with small droplets of blood visible. This was in addition to the use of topical minoxidil. The theory is one of two; either the light wounding cause stem cells to create new hair follicles instead of skin (much like follica’s procedure), or it allowed the minoxidil to penetrate more deeply into the dermis. This was done twice per week, NOT everyday. As to the possible infection aspect, all I can say is…DUH!!! Basic antiseptic procedures MUST be followed when doing a procedure like this, especially if blood is produced. Spraying the dermaroller with a high concentration of alcohol (perhaps EverClear), washing the scalp, then using a high quality antiseptic solution on the scalp prior to the treatment is an absolute MUST. I would not be at all surprised to learn that those who do indeed acquire post-rolling infections are not adhering to basic pre-procedure antiseptic techniques. I have been derma-rolling for the past 3 years with NO adverse bacterial effect.
Great comment: Yes, there is now published data suggesting that combining Minoxidil and a dermaroller can increase the effectiveness of Minoxidil.