Nylar and boric acid are two safe, natural and effective ways to control fleas in a dog house. A thorough cleaning combined with these treatments can kill any fleas in the doghouse and prevent it from becoming infested again.
To kill fleas inside a doghouse, clean the house thoroughly, and wash or destroy any dog bedding. Once the doghouse is clean, spray Nylar inside. Nylar is a flea treatment that prevents fleas from completing their full life cycle. It is a good choice for areas with hard flooring and remains effective for up to a year.
Sprinkle boric acid on clean dog bedding to kill any fleas that attempt to infest fabric inside the doghouse. Do not confuse boric acid with Borax, a chemical that is very toxic to dogs.
Clean the dog as well, and apply some flea control treatment before allowing it near the doghouse. If the doghouse is in a grassy yard, mow the surrounding area, and spray it with a pet-safe insecticide.