We cannot determine when DPHP concentrations peaked in cohort 1 because urine samples were collected at only two time points after polish application. In cohort 2, of the six participants who collected only 24 h of urine samples following nail polish application to fingernails, two exhibited peaks within the time frame, while four exhibited maximum urinary DPHP in their final samples, suggesting that DPHP concentrations may have peaked after completion of urine collection for these individuals (Fig. 4). Three of the four participants who collected 48 h of urine samples exhibited peaks in urinary DPHP concentrations between 10 to 20 h post-nail polish application (Fig. 5). The maximum urinary DPHP concentration of the fourth participant who provided 48 h of samples occurred in their final sample. In the control and glove painting phases, urinary DPHP concentrations over 24 and 48 h were lower and showed less variability compared to the nail painting phase for the majority of participants, although some aberrations were observed (Fig. 4 and Fig. 5). Differences between individuals in rates of uptake, metabolism, excretion or residual confounding by other exposures to TPHP may have contributed to the variability observed in urinary DPHP concentrations over time. Unfortunately we did not collect information on personal characteristics that may be related to these factors such as race and ethnicity, body mass index or other environmental exposures (e.g. smoking and tobacco use).