Topical Tretinoin Use for Photodamage [editorial]

Skin aging is caused by intrinsic genetic determi­nants combined with the influence of extrinsic environmental factors. Progress has been made in understanding the mechanisms behind photodamage. UV-induced changes in the nuclear and mitochondrial DNA, oxidative stress with the generation of reactive oxygen species, and chronic subclinical inflammation from exposure to UV radiation all have been implicated as plausible etiologies.