The measurement of hair cortisol is increasingly used to measure long-term cumulative cortisol levels and investigate its role as an important stress mediator. In this study a comparative statistical analysis of six independent studies (all analyzed in our laboratory) was performed to propose normative baseline values for cortisol in hair and evaluate potential influences of sex, age and hair color. Cortisol concentrations in hair of 554 subjects were measured and a comparative statistical analysis was performed. The analysis showed that cortisol levels significantly differ depending on age. The toddler group (7 months to 3 years) showed significantly higher values (median 10 pg/mg, p-value < 0.0001) than the adolescent group. The adolescent group showed significantly lower (p-value < 0.0001) values (median 2.4 pg/mg) than the adult group (median 5.8 pg/mg). Furthermore, in the adult group men showed significantly higher values than women (p-value < 0.05).This effect could not be seen in the adolescent group. Black hair showed higher cortisol concentrations than blond hair (p-value < 0.0001). An interlaboratory comparison for hair cortisol between three laboratories revealed very consistent results.