What is the whitening ingredient in the pen? How does it work? June 17, 2021 13:32 Updated The enamel safe formula contains 3% hydrogen peroxide, a professionally recommended whitening ingredient. Related articles Can I use this with a mouth guard or Invisalign type of braces? Do my teeth have to be dry before doing the treatment? Am I allowed to eat or drink after application? Do you need to brush your teeth before eating in the morning after using the pen? What age range is hum kids by Colgate smart manual toothbrush suitable for? Comments 0 comments Article is closed for comments.