We're glad you reached out about this and hope it helps to know that this tooth discoloration is actually a sign your mouthwash is working, and that the discoloration is reversible and preventable. Crest Pro-Health products contain active ingredients that are recognized as safe and effective, and are optimized to fight plaque and gingivitis. After they kill the germs in your mouth, the germs may collect on the tooth surface and create the appearance of a brown stain. To help aid in the removal of tooth surface stain, we recommend a tartar-control/whitening toothpaste, a power toothbrush, floss, and regular dental visits. When you have a minute, please reach out to us at (800) 285-9139 and let us know if any of the tips have helped