Table 1.

Effects and mechanisms of collagen and related substances on skin aging.

Source	Substance	Dosage	Method of Administration	Experimental Material	Role	Mechanism	References
Animals (cows, chickens, pigfish)	Collagen	2.5 g/d to 10 g/d (collagen hydrolysate), 3 g/d (collagen tripeptide)	Oral	Human skin	Improves skin quality, improves smoothness and elasticity, and wrinkles and fine lines are reduced	Collagen fibrous tissue ↑, skin moisturizing ability ↑, water loss ↓, skin redness and inflammation ↓	[20,21]
Animals (cows, chickens, pigfish)	Collagen hydrolysate		Oral	Uva-induced human skin fibroblasts (ESFs)	Skin structure is improved and collagen synthesis is promoted	Activating the TGF-β/Smad pathway, AP-1, MMP-1, and MMP-3 express ↓, free radical content ↓	[25]

↑, increase; ↓, decrease.