Advances in Aging Research, 2014, 3, 265-284 Published Online September 2014 in SciRes. http://www.scirp.org/journal/aar http://dx.doi.org/10.4236/aar.2014.34036 How to cite this paper: Gragnani, A., Cornick, S.M., Chominski, V., de Noronha, S.M.R., de Noronha, S.A.A.C. and Ferreira, L.M. (2014) Review of Major Theories of Skin Aging. Advances in Aging Research, 3, 265-284. http://dx.doi.org/10.4236/aar.2014.34036 Review of Major Theories of Skin Aging Alfredo Gragnani 1* , Sarita Mac Cornick 2 , Verônica Chominski 2 , Samuel Marcos Ribeiro de Noronha 2 , Silvana Aparecida Alves Corrêa de Noronha 2 , Lydia Masako Ferreira 2 1 Division of Plastic Surgery, Department of Surgery, Federal University of Sao Paulo, Paulista School of Medicine (UNIFESP-EPM), Sao Paulo, Brazil 2 Division of Plastic Surgery, Department of Surgery, UNIFESP-EPM, Sao Paulo, Brazil Email: * alfredogf@ig.com.br Received 4 June 2014; revised 9 July 2014; accepted 19 August 2014 Copyright © 2014 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract Here we aim to describe each factor that leads to skin aging and describe their mechanisms. A PubMed database searches (from January 2004 to March 2014) using aging and skin as searched terms. There are substantial evidences showing that aging is associated with damage from free radicals represented by various reactive oxygen species (ROS). Mitochondria are producers and also targets of oxidative stress. The cycle of mitochondrial dysfunction can trigger the aging pro- cess. In the cellular senescence and telomeres theory, the diploid cells exhibit a limited prolifera- tion potential. After a finite number of divisions, they enter a state of senescence with a stop rep- lication in cell proliferation. It is suggested that aging is associated mainly with hyper-regulation of apoptosis. Obesity presumably accelerates the process of aging, which is aggravated by smoking. And the influence of the environment, called solar UV irradiation is of considerable importance to skin aging. There are several mechanisms that trigger the natural aging process and contribute to age-related changes, including oxidative stress theory of free radicals, the mitochondrial dysfunc- tion, telomere shortening, UV radiation and other mechanisms that taken together or alone may or not accelerate the change in skin. Keywords Aging, Genetics, Reactive Oxygen Species, Telomerase, Cell Senescence 1. Introduction The skin acts as a protective barrier between the internal organs and the body and the environment. It is divided * Corresponding author.