Have veneers, but want them whiter. Can I use gel to bleach my real teeth underneath?

Yes.....MAYBE! Porcelain veneers get their resulting color determined by the color of the porcelain, thickness of the porcelain, opacity or translucency of the porcelain and THE COLOR OF THE UNDERLYING TEETH. Thus, if you have thin veneers and they aren't opaque, bleaching the back side of the teeth that are veneered may lighten them up somewhat. However, I wouldn't hold my breath that you are going to get the veneered teeth considerably whiter.Porcelain veneers themselves are very color stable, they don't usually get darker or change color over time. The best way to insure getting the color you want is to have them redone by an experienced and reputable cosmetic dentist, and make sure you see and approve of the color before you accept them and he bonds them into place.

Sorry. Once the Veneers are bonded onto your teeth, they cannot be made any whiter, even with gel bleach.

If you would like to change the color of your veneers then you will need
to replace them. There is a color cero you should try. That would be a color
that i think you are looking for and would look great. A sparkling smile!