How long before sun exposure should sunscreen be applied?

Several articles confirm that sunscreen should be applied evenly and generously to all exposed areas 15 to 30 minutes before sun exposure so that the sunscreens can be fully functional. However, this recommended time interval is based on how sun care products have been tested. Indeed, sunscreen testing protocols require a drying time of 15 to 20 minutes before the start of the sun protection factor test to ensure water resistance. Thus, the labeling reflects this instruction, but no data suggests that the effectiveness of the sunscreen is delayed.

However, a recent study aimed to determine how long it takes for a sunscreen to provide optimal protection after uniform application. To do this, an analysis in vitro of spectral transmittance and an analysis in vivo using UV photography were conducted on five healthy volunteers of phototype III. The results show that the sunscreen is active as soon as it is applied. However, it takes 5 to 10 minutes before the sunscreen stabilizes.

Recommendation : It has been demonstrated that sunscreen products have a satisfactory absorption capacity within shorter time frames. Therefore, in practical terms, it does not seem necessary to wait more than 10 minutes before exposing oneself to the sun, coupled with a new application every 2 hours thereafter if necessary. However, this standard recommendation is prudent to ensure good water resistance during swimming, or to maintain its photoprotective properties intact after exposure to water.