There’s also the issue of where the growth factor can come from. In 2018, Sandra Bullock and Cate Blanchett caught flack for talking about a $650 “penis facial” they had gotten at celebrity aesthetician Georgia Louise’s spa. The growth factors used in the serum were “derived from the progenitor cells of the human fibroblast taken from Korean newborn baby foreskin.” SkinMedica’s serum also uses growth factor proteins that are lab-created but were derived from the stem cells of a single neonatal foreskin over 20 years ago. But if you’re curious about growth factors and would rather not use anything connected to human cells, opt for a plant-based product.