Scheme of the hypothesised redox-dependent mechanisms of CELERGEN physiological effects. Marine collagen peptides (MCPs) easily penetrate gastrointestinal wall (GI, three arrows) and through blood circulation are mainly deposited in the skin. Antioxidant component of the nutraceutical is partly metabolised in GI thus possessing low bioavailability (one arrow); however, skin-targeting antioxidants and their metabolites reach different skin layers. While in the circulation, MCPs stimulate blood phagocytes (granulocytes and monocytes) and endotheliocytes (E) to produce reactive oxygen species (ROS) and reactive nitrogen species (RNS) by activating Toll-like receptors 4 (TLR4). Hydroxyproline (HYP) and prolyl-hydroxyproline (Pro-HYP) dipeptides as major components of MCPs are metabolised by corresponding oxidases and hydroxyl radicals are formed as by-products. Antioxidants prevent systemic oxidative stress blocking GSH oxidation, GPx, GST, and SOD3 activation. In the skin, collagen synthesis and deposition as well as elasticity are increased while (hypothetically) low levels of oxidised forms of skin lipids such as unsaturated fatty acids (PUFA-ox), squalene (Sq-ox), malonyl dialdehyde (MDA), and 4-hydroxy-2-nonenal (4-HNE) may facilitate cell signalling for ATP synthesis and sebum production.