Saliva

• Saliva from human spit is probably the cheapest natural lens defogger. To use defogger to clear a lens, you spit on it and wipe with a cloth. After you rub it around your mask, rinse with water. Use saliva as a last resort, however, because bacteria found in human saliva can lead to health problems and queasiness. Alternatively, you can lick the inside of the goggles. Just don't touch the lens because the oils on your fingers can cause smears.
  
  

Toothpaste

• Toothpaste defogs lenses, as long as it's not gel. To use toothpaste as a defogger, rub the toothpaste in circles all over the lens. This is especially helpful on swim goggles and scuba masks because it removes any silicone film. If the lens aren't scratch resistant, make sure to rub with extra care to avoid scratches. After you've rubbed the toothpaste over the lens, rinse with clear water to get rid of film. The lens should be clear and fog-free.
  
  

Soap

• Soap used to wash your dishes can help defog lenses as well. To use this method, you simply place a small dot of soap on both lenses of your mask or goggles, and spread it around with a paper towel. After you rinse the lenses in cold water, some of the soap remains on them, creating a layer to get rid of fog.
  
  

Vinegar

• Vinegar mixtures are used to keep mirrors and glass fog-free. For this method, first clean the lens with a mixture of one quart room-temperature water and two tablespoons white vinegar. Dry the lenses before applying another layer of two tablespoons vinegar mixed with hot water. After the last layer, don't dry the lenses to create an anti-fog layer.