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Comparison of chronological aging and photo-aging of the skin. In the figure, "↑" means "rise or increase"; "↓" means "fall or decrease"; DNA= deoxyribonucleic acid; ECM= extracellular matrix; UVRs = ultraviolet radiations; ROS= reactive oxygen species; MMPs = Matrix metalloproteinases; HA= Hyaluronic acid.
