A sweating toilet bowl can cause mildew and mold growth in your bathroom.
Toilet bowls sweat because the air around the toilet is considerably warmer than the temperature of the toilet water. This creates condensation and causes the toilet to sweat.
You can purchase an anti-sweat toilet kit to insulate the tank and reduce condensation.
The kits are inexpensive, easy to install, and are very effective.
Liners are applied with an adhesive to the inside of the tank. They are nearly permanent, and will require some effort to remove. Most anti-sweat toilet kits are universally sized to fit the dimensions of most toilets.
Simply covering your toilet tank with a fuzzy cover will help insulate it and will cut down on condensation.