The effects of an application of suncream on selected physiological variables during exercise in the heat

The purpose of this study was to investigate the effects of an application of suncream on mean skin temperature (MST), rectal temperature (Tre), oxygen consumption and heart rate during exercise in the heat.

Twenty-two male subjects underwent two steady state exercise tests (55% of maximum oxygen consumption, mean work rate 153 watts) for 40 minutes (following a 5 minute warm-up), under two treatment conditions at the same ambient temperature (32 degrees C, 54% relative humidity). One treatment involved wearing an application of suncream (SC) while the other treatment did not (NSC). Suncream was applied in the amount of 30 ml/m2 of body surface area.

Results of this study indicated that an application of suncream significantly reduced MST, on average. 31 degrees C, during exercise in the heat (p = 0.03). However, further statistical analysis revealed that this was a function of a significant interaction effect (p = 0.001) (main effect is sunscreen; interaction effect sunscreen plus temperature). MST was lower for the SC condition versus NSC over all time measurements. Results also showed a significant difference in the mean core to skin temperature gradient (p = 0.001), with a greater gradient existing in the SC condition. There did not appear to be any effect of suncream on ventilation, rectal temperature, oxygen consumption, lactate levels, sweat loss, percent plasma volume change, rating of perceived exertion, or respiratory exchange ratio. Interestingly, although not statistically significant (p = 0.18), rectal temperature remained lower, on average 0.1 degree C, under the SC condition for every measurement throughout the exercise session.

In conclusion, results of this preliminary study suggest that an application of suncream does not impair heat dissipation as indicated by a decreased MST and increased core to skin thermal gradient.