[Science] Preservatives in Sheet Mask Damage Skin Barrier + Keeping Masking Under 20 Minutes

 

[NIH] A couple of years old and found by Sol, but I thought it was fascinating to see an experiment done on length of sheetmask application. The skincare enthusiast circles tend to recommend not leaving a sheetmask on beyond it getting dry because it feels awful and (speculation) the dry mask would start dehydrating your skin.

This research team of Zhou et al. found that on average, sheetmasking longer than 20 minutes seems to "drive the exposure to hazardous chemicals to increase significantly." Testing was done on 139 Chinese people (30 males, 109 females) of the average age of 44 of all different skin types across 2 months in a temperature and humidity controlled room.

I thought this paragraph was extra interesting:

While most facial sheet masks recommend a 15–20 min application time, the scientific rationale behind this recommendation is still unknown. It is easy to accept that an appropriate application time means at which point the absorption of active ingredients reaches a peak while the exposure to hazardous substances remains at low level. From this perspective, our data may for the first time provides a scientific base for recommending the appropriate application time. In the present study, applying facial sheet masks for longer than 20 min drove the exposure to preservatives to a dramatic increase. This further reminded us that in a realistic risk assessment, use of amount per application may underestimate the exposure to facial sheet masks if masks are applied for longer than 20 min. Therefore, we not only recommend consumers to apply facial sheet masks for less than 20 min to ensure safety, but also risk assessors to take caution in assessing risks associated with an application time of longer than 20 min. We hypothesized that the evaporation of water when applying the masks on the face made preservatives concentrate in the mask, and when the application time went up to more than 25 min, the skin started to absorb chemicals fast from the sheet due to the concentration difference between the sheet and facial skin.

Keep in mind the research found variances across different mask types as well as participants' genders, skin types and how well the sheetmask fits the face (ie: whether or not it caused folds), so again, YMMV. 20 min is the average. Additionally, it was a study done in China, on Chinese participants, and the researchers mention that they believe their study could be generalized for East Asians, citing a consistency with a Japanese study. While r/AB has always stressed YMMV and that we share more in common than differences across genders and races, there are differences when you get to the nitty gritty, but not enough to matter for someone just starting out in skincare. And with all the information and misinformation out there, why bog someone down with this info early on. 

This all started when marcelavy linked two Japanese cosmetic chemists on Twitter/X discussing preservatives in sheetmasks: @natsunatsu_7722 and @hikaricosme11. Main TIL between the two accounts in their early May 2024 is that the preservatives in sheet mask damage the skin barrier to allow better penetration, and that using too many sheetmasks may deteriorate your barrier over time. So ideally when using sheetmasks, use them in moderation and choose the single pack sheetmasks over bulk (like the ones lululun offers) that require less preservatives than a bulk one. Obviously YMMV, you may have a strong barrier.

I should probably stress that preservatives are important to preserve your skincare products, so don't demonize them from this. Dose makes the poison: drinking water everyday is healthy (and a necessity), drinking 80 gallons of water everyday is not.