Yes, you can use a little bleach with our white towels; however, we don't recommend doing this often because bleach can weaken cotton fibers over time. Since washing in hard water may cause graying, we would suggest adding a cup of vinegar to your wash water if you live in an area with hard water. You can also soak your towels in a lemon juice and water solution, wring them out and let them dry in the sun to naturally whiten them. Then wash and dry normally.
You can also read more tips about naturally whitening your towels here.