There are three types: strips, brush-on gel and toothpaste.

Strips are easiest since you can do other things while wearing them, and Perioe's one-week pack has 14 strips. Gels need to follow the instructions, and VUSSEN 28 is a big tube. For an all-in-one, see the Olive Young-exclusive 4-week whitening set with gel and toothpaste (5,819 reviews). Read the directions first, especially with sensitive teeth.