In high humidity, the tabs may develop small dark spots. The humidity is absorbed by the xylitol and clay in the tabs and creates the spots. This happens when the tabs are exposed to big temperature changes, such as in your bathroom and/or when the bottle is left open for long periods of time. Normally this problem is counteracted with synthetic chimicals, but since we refuse to use them, this is a harmless side effect and in no way affects the quality of your Natch Tabs. So in short, the tabs are safe. Continue to enjoy Natch