Tattoos do not affect exercise-induced localised sweat rate or sodium concentration

Abstract

Objectives: Skin tattoos have been shown to reduce localised sweat rate and increase sweat sodium concentration ([Na⁺]) when sweating is artificially stimulated. This study investigated whether similar responses are observed with exercise-induced sweating.

Design: Unblinded, within-participant control, single trial.

Methods: Twenty-two healthy individuals (25.1±4.8 y (Mean±SD), 14 males) with a unilateral tattoo ≥11.4cm² in size, ≥2 months in age, and shaded ≥50% participated in this investigation. Participants undertook 20min of intermittent cycling (4×5min intervals) on a stationary ergometer in a controlled environment (24.6±1.1°C; 64±6% RH). Resultant sweat was collected into absorbent patches applied at two pairs of contralateral skin sites (pair 1: Tattoo vs. Non-Tattoo; pair 2: Control 1 vs. Control 2 (both non-tattooed)), for determination of sweat rate and sweat [Na⁺]. Paired samples t-tests were used to determine differences between contralateral sites.

Results: Tattoo vs. Non-Tattoo: Neither sweat rate (Mean±SD: 0.92±0.37 vs. 0.94±0.43mg·cm^-2·min^-1, respectively; p=0.693) nor sweat [Na⁺] (Median(IQR): 37(32-52) vs. 37(31-45) mM·L^-1, respectively; p=0.827) differed. Control 1 vs. Control 2: Neither sweat rate (Mean±SD: 1.19±0.53 vs. 1.19±0.53mg·cm^-2·min^-1, respectively; p=0.917) nor sweat [Na⁺] (Median(IQR): 29(26-41) vs. 31(25-43)mM·L^-1, respectively; p=0.147) differed. The non-significant differences for sweat rate and [Na⁺] between Tattoo vs. Non-Tattoo were inside the range of the within participant variability (sweat rate CVi=5.4%; sweat [Na⁺] CVi=4.4%).

Conclusions: Skin tattoos do not appear to alter the rate or [Na⁺] of exercise-induced sweating. The influence of skin tattoos on localised sweat responses may have previously been over-estimated.

Keywords: Eccrine gland; Fluid loss; Physical activity; Thermoregulation.