3. Scrub your nails with whitening toothpaste. The same ingredients in whitening toothpaste that help whiten teeth, which are keratin-based, can also help whiten nails, which are also keratin-based. 1  Apply the toothpaste to each nail, using a pea-sized dollop or less for each.ry a lemon juice and baking soda paste. Combining lemon juice with a bit of baking soda can form an even more powerful cleansing paste for your nails. 1  Mix 1 Tbsp (15 ml) lemon juice with 2 to 3 Tbsp (30 to 45 ml) baking soda. 2  Stir together in a small plastic or glass dish until a paste forms.