Why Does Natalia Spierings Say Rubbing Collagen Peptides Onto Skin Does Not Work?

Dermatologist Natalia Spierings says rubbing collagen or collagen peptides onto skin with a face cream does not work. The peptide is too big to penetrate deep down to where collagen lives. She says the peptide is like an elephant trying to squeeze through a dog flap door in a patio door. Collagen in a fancy moisturizer stays on the skin until it washes away.