... ingredients of the pen is a kind of peroxide,hydrogen peroxide or carbamide peroxide or non peroxide. any concentration of 2ml, 4ml, any ml,hp ... non peroxide available. soft applicator brush.to use the pen, just twist the bottom of the the pen to release some gel ... on the teeth surface. after 15 minutes, wipe off the gel and rinse the mouth.easy to take with, whiten teeth ...