All sheet masks are different and contain different ingredients, which can alter the answer, therefore we recommend checking the pack. In general, the recommendation is to apply it for 20 minutes, so make sure to sit back and relax, maybe with the TV on and allow the ingredients to take action.
Many people make the mistake of thinking longer it is applied to the skin, the better the effect will be, which actually isn’t the case. While 20 minutes are needed for it to take action, if it is on the skin for too long then it can have the reverse affect. Think of it from two angles. Firstly, the sheet mask is meant to help hydrate the skin, however if it is left so long that it dries out then it can have the reverse affect and actually start to suck out the moisture from the skin. Secondly, it is creating a barrier on the skin therefore if left on too long it could irritate. Regarding the dryness of the mask, just make sure when you are taking it off, it is still damp and it hasn’t dried up completely, as this is a clear sign it has been too long. Some people have reported falling asleep while wearing sheet masks, therefore this is something we highlight to be cautious about.
For these reasons, and through a number of brands testing their products, a 20 minute waiting time seems to be the golden number and the general rule of thumb.