Toothpastes and other dental products that contain peroxide are safe to use and can help whiten teeth. However, combining hydrogen peroxide from your medicine cabinet with toothpaste to make a homemade teeth whitener is not recommended. Peroxide in toothpaste and other dental products bleaches teeth to make them whiter. However, the concentration of peroxide in these products is low and carefully controlled. Making your own teeth whitener with toothpaste and hydrogen peroxide could expose your mouth to too much peroxide, which may cause irritation and other problems. It's always a good idea to talk to your dentist before using teeth whitening products.