Purpose: Although numerous articles have addressed the role of different factors on aging, sufficient scientific evidence has not been offered to support many of the statements. The purpose of this research study was to investigate the role of environmental factors on facial aging in identical twins.

Methods: Participants were recruited at the Twins Day Festival held in August, 2006. This festival is held annually in the city of Twinsburg, Ohio and is attended by approximately 3000 pairs of twins. After obtaining IRB approval, our research team interviewed 99 pairs of identical twins. They also completed questionnaires and digital images of each twin were obtained. The images were standardized and matched for color, size, and lighting. A four member panel independently estimated the age difference between each identical twin pair. The age differences were correlated with the various environmental factors. The results (averaged across the 4 raters) were statistically analyzed using multiple linear regression methods. The full linear model was generated and stepwise methods were employed to reduce the model to the statistically significant features.

Results: For every 4 point increase in BMI rating, a female was perceived to be about 1 year younger (p < 0.005) compared to her twin. As an example, a female with a 20 point higher BMI rating was perceived to be 5 years younger than her twin. A twin who had received hormone replacement therapy for 13 years was perceived to be 1 year younger than her twin who did not. On the other hand, a female with a history of skin cancer was perceived to be almost 4 years older than her twin who has not had skin cancer (p < 0.01). A female who has smoked for at least 5 years was perceived to be 1 year older than her non-smoking twin (p < 0.0005). A female with 8 hours more sun exposure per week compared to her twin was perceived to look 1 year older (p < 0.005). When the subcutaneous volume was taken into consideration, a female with a higher BMI had a higher perceived facial subcutaneous volume rating than her twin (p < 0.025). A female who had a history of skin cancer or who smoked had a lower perceived facial subcutaneous volume rating compared to her twin who did not have skin cancer (p < 0.01) or who did not smoke (p < 0.0005). A female who had received hormone replacements for several years had a higher perceived hair quantity rating compared to her twin who had not used hormones (p < 0.0005). A female with a higher BMI had a better perceived skin color rating compared to her twin (p < 0.01), while a female who smoked had a lower perceived skin color rating compared to her non-smoking twin (p< 0.0005). A female twin with a history of skin cancer had worse wrinkling (p < 0.0005), as did the female twin who smoked (p < 0.0005).

Conclusion: This study identifies several environmental determinants that play a role in facial aging in identical twins. Some of these include smoking, sun exposure and history of skin cancer which increase perceived facial age, and increases in BMI and hormone use which decrease perceived facial age.
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