Biostimulators are compounds such as Calcium hydroxylapatite that are injected into the skin to stimulate the production of collagen and elastin, proteins that help skin stay firm and flexible. Collagen is responsible for the skin's structure and elasticity. As people age, their bodies produce less collagen, which can cause wrinkles, sagging, and loss of skin volume. Biostimulators can help slow down the aging process and increase volume.