Q: I previously read somewhere that when fasting, you are allowed to use toothpaste and mouthwash as long as it is not swallowed. Is this correct?
A: The use of toothpaste and mouthwash would render the fast Makrooh and impermissible (i.e. the fast will be devoid of any reward). The Sunnat is to use the Miswaak which is allowed during fasting.