What happens in the skin.
"Firming" creams nourish the epidermis. Collagen is in the dermis and hypodermis. The collagen molecule is too large to pass through the skin barrier topically: that's physics, not a formulation flaw.
Lutronic's Genius RF delivers radiofrequency at a depth of 2.5 mm through microneedles. The heat targets existing collagen and triggers a repair response that lasts 6 months. HIFU goes even further: it reaches the SMAS at 4.5 mm, the same layer as a surgical facelift, without an incision.
Collagen doesn't pass through the skin. You have to go and get it where it is.