Derma-roller/pen hair growth treatment relies on genes that promote the development of new hair cells. This takes place within the hair follicles, the minor openings that cover the scalp as well as the rest of the body. A number of chemicals are needed to trigger the production of hair cells, and one of the most important of these is the human growth factor.
More specifically, the derma-roller/derma-pen (depends on the case) work by activating the production of hair growth factor. When the medical device rolls along the skin, causes minor surface wounds to the tissue, thus the body has to produce the hair growth hormones and other chemicals assist and stimulate the growth of hair in the affected area.