Comparing Facial Aging Between Identical Twins With 3D Imaging

This is a prospective, observational, single-site study conducted at the Twins Days Festival, Twinsburg, Ohio (August 8-9, 2026). The design revisits the 2009 identical-twin facial aging study of Guyuron and colleagues with two methodological advances: replacement of standardized two-dimensional photography with three-dimensional facial surface imaging, permitting objective quantitative measurement of volumetric and topographic facial differences, and inclusion of GLP-1 receptor agonist and other rapid weight-loss medication exposure as a facial-aging variable that did not exist as a widespread exposure at the time of the original study.

Participation is completed in a single session. After eligibility screening and written informed consent, each twin independently completes a structured questionnaire covering demographic, lifestyle, environmental, and medical-history domains, and undergoes standardized 3D facial surface imaging using a non-contact, non-ionizing optical system (approximately 1-2 minutes per participant). A staff member records Fitzpatrick skin type by brief visual assessment. No intervention is administered, no biological specimens are collected, no genetic testing is performed, and no individual results are returned. Zygosity is established by participant self-report, supported where available by prior DNA testing or physician confirmation; self-reported dizygotic or zygosity-uncertain pairs are recorded as such and analyzed separately from the confirmed monozygotic cohort.

All data are recorded against coded participant identifiers. Because each monozygotic pair serves as its own genetic control, the primary analysis is of within-pair differences in quantitative 3D facial measurements, correlated with discordance in self-reported exposures. For the secondary objective, twin pairs discordant for self-reported GLP-1 receptor agonist use are compared with respect to midface and lower-face volume and contour. All measurement, extraction, and analysis of study data are performed by the study team on coded data.

Inclusion criteria

• Adults aged 18 years or older
• Members of a monozygotic (identical) twin pair, with both twins present and willing to participate
• Able to provide written informed consent in English

Exclusion criteria

• Age under 18 years
• Inability or unwillingness to provide informed consent
• Facial conditions or recent facial surgery that, in the investigator's judgment, would prevent standardized imaging
• Pregnancy, by self-report

Note: Zygosity is established by participant self-report, supported where available by prior DNA testing or physician confirmation. No genetic testing is performed and no biological specimens are collected. Pairs who self-report as dizygotic or are uncertain of their zygosity are recorded as such and analyzed separately from the confirmed monozygotic cohort.