If your diapers start repelling moisture, then you know the zinc oxide is not washing out of the diapers. You'll know you're having repelling if your LO starts leaking wetness even though the diaper doesn't appear to be very wet. It has a waterproofing effect, which is the last thing you want for diapers. But for us, with plain cotton diapers we used it with no trouble, because it washed out. It was only a problem on synthetic diapers, like pockets, because those didn't wash clean. You can get it out, if it is causing problems, by handwashing very vigorously with Dawn dish detergent-- you may need a scrubbing brush to help with the job.