Stem cells are pluripotent which means they have the ability to become any other type of cell. Human-derived stem cells can come from fetuses, chord blood, or adult adipose tissue. Osmosis preferes to utilize the adult sources because it is the most ethical. Stem cells are not typically used in skincare because no one would want someone else's cells rubbed into their skin. However, some people do use their own stem cells in certain procedures like facelifts with positive results.
Fibroblasts are only used as a source of growth factors. Osmosis combines stem cells and fibroblasts in a medium so that the stem cells can be encouraged to make growth factors similar to fibroblasts. Without that influence, stem cells don't necessarily make growth factors. The combination is the most powerful way to encourage the most complete growth factor population.