What if your dentist gave you a prescription for nystatin cream she told you to clean and dry your upper denture then apply cream to denture then put denture in your mouth on the tube it says for exte?

Apparently you have some type of yeast infection in your mouth. Your denture is contributing to the problem. A small amount of nystatin will not be harmful if swallowed. Make sure you take the denture out at night when you sleep. After a few weeks, the infection should clear up and you can stop using the cream. Let your dentist know if the infection does not clear up.