Multiple regression analyses to determine the effect of sweating rate and tattoo characteristics on sweat outcome measures during exercise

PURPOSE: To compare local sweating rate (LSR) and local sweat sodium ([Na(+)]), chloride ([Cl(−)]), and potassium ([K(+)]) concentrations of tattooed skin and contralateral non-tattooed skin during exercise. METHODS: Thirty-three recreational exercisers (17 men, 16 women) with ≥ 1 unilateral permanent tattoo on the torso/arms were tested during cycling, running, or fitness sessions (26 ± 4 °C and 54 ± 13% relative humidity). Forty-eight tattoos with a range of ink colors, ages (3 weeks to 20 years), and densities (10–100%) were included. Before exercise, the skin was cleaned with alcohol and patches (3 M Tegaderm + Pad) were placed on the tattooed and contralateral non-tattooed skin. LSR was calculated from sweat mass (0.80 ± 0.31 g), patch surface area (11.9 cm(2)), and duration (62 ± 14 min). Sweat [Na(+)], [Cl(−)], and [K(+)] were measured via ion chromatography. RESULTS: Based on the analysis of variance results, there were no differences between tattooed and non-tattooed skin for LSR (1.16 ± 0.52 vs. 1.12 ± 0.53 mg/cm(2)/min; p = 0.51), sweat [Na(+)] (60.2 ± 23.5 vs. 58.5 ± 22.7 mmol/L; p = 0.27), sweat [Cl(−)] (52.1 ± 22.4 vs. 50.6 ± 22.0 mmol/L; p = 0.31), or sweat [K(+)] (5.8 ± 1.6 vs. 5.9 ± 1.4 mmol/L; p = 0.31). Multiple regression analyses suggested that younger tattoos were associated with higher sweat [Na(+)] (p = 0.045) and colorful tattoos were associated with higher sweat [Cl(−)] (p = 0.04) compared with contralateral non-tattooed skin. Otherwise, there were no effects of LSR or tattoo characteristics on regression models for LSR or sweat electrolyte concentrations. CONCLUSION: There were no effects of tattoos on LSR and sweat [K(+)] during exercise-induced sweating, but tattoo age and color had small effects on sweat [Na(+)] and sweat [Cl(−)], respectively. CLINICAL TRIAL IDENTIFIERS: NCT04240951 was registered on January 27, 2020 and NCT04920266 was registered on June 9, 2021.