1. Kligman AM, Zheng P, Lavker RM. The anatomy and pathogenesis of wrinkles. Br J Dermatol. 1985;113:37–42.
2. Piérard GE, Uhoda I, Piérard-Franchimont C. From skin microrelief to wrinkles. An area ripe for investigation. J Cosmet Dermatol. 2003;2:21–28.
3. Ekman P. The Face of Man: Expressions of Universal Emotions in a New Guinea Village. New York: Garland, 1980.
4. Twain M. [Samuel Langhorne Clemens] in Following the Equator. 1897.
5. Hillebrand GG, Levine M, Miyamoto K. The age-dependent changes in skin condition in ethnic populations from around the world. In: Berardesca E, Leveque JL, Maibach HI (eds) Ethnic Hair and Skin, 1st ed. New York: Infoma Healthcare, 2007, pp. 105–122.