Dermatologists believe inactive ingredients not listed on skin care brand Yes To’s recalled Grapefruit Vitamin C Glow-Boosting Unicorn Paper Mask may be the cause of burning and blistering skin among some of its users.

The mask, which was sold at Target and Ulta and marketed to the teen and tween crowd, was recalled earlier this week after customers said it caused burns and blisters. It lists water, aloe barbadensis leaf juice, methyl gluceth-20 and glycerin as some of its main ingredients in addition to Vitamin C, but dermatologists suggest an unlisted acid could be what’s behind the skin burning.