In February 2023, TikTok users reported rancid odors and skin irritation from Kosas Revealer Concealer, while an older Reddit post alleged black spots, a blue-cheese smell and burning more than a year after opening. Kosas said its preservatives and stabilizers prevent mold and pathogens; the company also said discoloration in one video showed product separation. Chemists raised questions about formula stability, but mold was not confirmed.
Sources
https://www.yahoo.com/news/allegations-mold-kosas-concealer-customers-001341009.html
The brand has also been directly responding to some of the criticism in TikTok comments. When one user posted a video of her concealer and questioned if the discoloration in the product was mold, the Kosas brand account clarified that it was just the concealer separating and "clinging to the sides" of its packaging.