Tattooing is Mainly Cultural: A Representative Twin Study of Tattooing Determinants.

Tattooing has become increasingly common in recent decades, yet little is known regarding factors that influence tattoo behavior. Sources of influence will be important, for instance in aiding studies of long-term health effects. From the population-based Danish Twin Tattoo Cohort established in 2021, the study included 9,173 randomly selected twins born 1920-2004. Among these were 4,790 (52%) responders to a questionnaire on tattooing and lifestyle factors. There were 55% females, 22% were monozygotic twins, and the median age was 51 years. Shared influence of tattooing over time was assessed by comparing monozygotic and dizygotic twin pairs. Responders were population representative on sex, age, and lifestyle factors. The cumulative incidence of being tattooed before age 25 years increased markedly from 6% (95% CI: 4-7%) for males and 0% (0-1%) for females born in 1925-1960 to 30% (25-35%) for males and 41% (37-46%) for females born in 1981-2004. Tattooing was over twice as common among ever smokers compared to never smokers born in 1981-2004 (average smoking effect at age 25 years: 36% (29-43%)). The likelihood of a twin getting tattooed if the co-twin is tattooed, was 2.0 (1.4-2.6) and 1.8 (1.5-2.2) times higher, for monozygotic and dizygotic twins, respectively. The findings indicate that variation in the likelihood of becoming tattooed is primarily explained by shared environmental factors 65% (35-95%), and that genetic influences explained little of this variation. This study demonstrates that strong environmental exposures shared by twin siblings irrespective of degree of genetic relatedness drive the choice for getting tattooed. We conclude that tattooing is a cultural group clustering phenomenon that goes beyond genetically oriented behavioral characteristics.