Applying an insecticide directly to your pet is the quickest and most efficient way to kill fleas. One of the most famous products is Frontline Spray. These kind of sprays penetrate to the skin where most of the fleas are found. Once the insecticide comes in direct contact with the fleas, it will only take a few minutes for the fleas to die. Products that are applied to one spot on the coat, such as Advantage for dogs or cats, are also very effective in killing fleas. These products provide long term whole body protection.