Here are some great ways to prevent your snorkeling or diving mask from Fogging up while you are underwater.
Use toothpaste! This choice should be done before your first time in the water. This helps to eliminate the compounds which have stuck to the mask throughout the production process and causes fogging to happen. Rub the toothpaste around the interior of the mask using a cloth or paper towel. Do this for a couple of minutes. Also make sure it is not too gritty so that it does not scratch the lenses. After you are finished rubbing it around let it sit for ten minutes and then wash it away with fresh water.
Defogging wipes
There are especially formulated defogging wipes or anti-fog sprays on the market. The wipes go on tender, are invisible and may be used multiple times though there are other types too so be sure to follow the directions on the package.
Spray
When using the spray, then squirt it right on the inside of the goggles and rub it around before quickly dunking it under fresh water to wash. You should leave a little bit of residue behind to maintain the moisture from sticking to the lens.
You can combine your own anti-fog spray using whole face snorkel with a mixture of baby shampoo and water in a spray bottle. Baby shampoo is used since it is designed to be gentle on eyes, so that not only does your mask not fog but your eyes would not be irritated either. When all else has failed and you are out in the water you can spit inside the mask. This should work at least till you have other options available.
Other ways
If you do not mind spending a little extra cash then buy the new full Face snorkel mask that icon the market. It is specially designed not to fog. You are able to breathe through your mouth or nose, a complete face lens that provides you a bigger view; in addition, it includes a built-in shut off valve so that if you dip down into the water it closes the snorkel so that water does not come shooting in your mouth. These masks begin at about sixty dollars but involving the additional advantages, fewer pieces to get and keep an eye on this might be the thing to do.