1. US Census Bureau International Data Base World Midyear Population by Age and Sex for 2013 https://www.census.gov/population/international/data/worldpop/table_population.php
2. UN Population Division Towards Global Equity in Longevity. Population Facts 2012/2 http://www.un.org/en/development/desa/population/publications/pdf/popfacts/popfacts_2012-2.1.pdf
3. European Commission Median age of population, EU-27, 1990-2010 (1) (years).png. 2011 http://epp.eurostat.ec.europa.eu/statistics_explained/index.php?title=File:Median_age_of_population,_EU-27,_1990-2010_(1)_(years).png&filetimestamp=20111130143447
4. The aged epidermal permeability barrier. Structural, functional, and lipid biochemical abnormalities in humans and a senescent murine model;Ghadially;J Clin Invest,1995
5. Functional characteristics of the stratum corneum in photoaged skin in comparison with those found in intrinsic aging;Tagami;Arch Dermatol Res,2008