TABLE 1.

Histologic and biochemical differences between intrinsic and extrinsic aging.

Components	Intrinsic aging	Extrinsic aging	References
Epidermal HA	↓	↓ or ↔	Oh et al. (2011)
			Lee et al. (2016)
Dermal HA	↔	↑	Oh et al. (2011)
	Reduced extractability	Shortened length	Lee et al. (2016)
Dermal sGAGs	↓	↑	Oh et al. (2011)
		Clumped	Lee et al. (2016)
Proteins	Slightly altered structures	Markedly altered structures, Hydrophobic	Gniadecka et al. (1998)
Collagen fibers			Quan et al. (2004)
	↓	↑ or ↔	Li et al. (2013)
	Thinned, less soluble	Thickened, more soluble	Sharma et al. (2020)
	Fragmented, disorganized fibers		Chung et al. (2000)
	Decreased neocollagenesis, Type III to I ratio ↑		Wlaschek et al. (2021)
Elastic fibers	↓	↑ (Accumulation of altered fibers)	Bernstein et al. (1996)
			El-Domyati et al. (2002)
			Naylor et al. (2011)
			Bonta et al. (2013)

Abbreviations: GAG, glycosaminoglycan; HA, hyaluronic acid; sGAG, sulfated glycosaminoglycan.