Diatomaceous earth (DE) is a naturally occurring, siliceous rock that is crushed to a fine white powder. When a flea or tick crawls through the powder, it absorbs waxy outer layer of insects' exoskeletons, causing them to dehydrate. Diatomaceous earth does not kill flea eggs.
Diatomaceous earth is used both indoors and outdoors, but is typically not used directly on the dog or cat's skin because it is very drying.
However, food grade DE is sometimes used internally as a treatment for intestinal parasites. Dosages used by naturopathic vets are approx. 1 tsp per day for small dogs, up to 1 Tbsp per day for dogs over 55 pounds. When taken internally, DE is thoroughly mixed with food to avoid inhalation.
Food grade diatomaceous earth is available in many sizes for pest control.