Topical actives that affect the skin generally work in one of two ways. Some operate by signaling, supplying or prompting the molecules a cell uses to regulate itself. Others operate by controlled irritation, provoking a low-level stress response that speeds up cell turnover.
Retinoids are the most documented example of the second mode. They raise the rate at which skin cells are produced and shed, an effect often accompanied by redness, dryness, or flaking while the skin adjusts. The result follows from the turnover the irritation drives.
Growth-factor signaling belongs to the first mode. Rather than provoking a stress response, it presents the cell with a protein from the same family the tissue already uses to coordinate its activity. Core Biogenesis has described its own ingredients in these terms, as acting through cellular signaling pathways rather than the irritation that characterises retinoid mechanisms.
The distinction matters for two reasons documented elsewhere in the series. The mode of action determines what the active does at the cellular level, covered in Note 02, and it implies a different tolerability profile, since a signaling mechanism does not depend on provoking irritation to do its work. The protein at the centre of this mechanism still has to reach the follicle, which returns to the delivery question and to the fusion described next.