Treating fleas involves removing and killing existing adult and juvenile fleas. Flea products may address the egg, larvae and adult stages, but no insecticide can kill the cocoon stage. You must wait until it hatches to kill it. It takes 14 to 21 days for the lifecycle to be complete. It's best to start with natural, non-toxic interventions before proceeding to use harsh chemicals; in some cases you'll be able to eradicate fleas without any potentially harmful side effects.

Bathing puppies can get rid of existing fleas but won't necessarily keep them off. Be cautious of so-called "natural" flea products as they may still be dangerous for youngsters. Spray products do a better job and have some residual effect.

Products that contain insect growth regulators (IGRs) are the best choice for precise control because they prevent immature fleas from maturing into biting adults. They typically last a long time with a single application, some as long as seven months.

IGRs attack insects but not the pet and are one of the safest of the flea ingredients around. For instance, methoprene fools flea larva into thinking it’s a larva forever, so it never turns into a biting adult flea. Another early IGR called lufenuron (once-monthly pills for your pet) inhibits the development of the exoskeleton of the flea and sterilizes the bug so it can’t reproduce. Pyriproxyfen (Nylar) works like methoprene but with an increased potency that also kills flea eggs and larva.

A better understanding of flea biology also helped researchers to develop active ingredients that attack the flea nervous system. These include fipronil (Frontline), imidacloprid (Advantage), nitenpyram (Capstar), and selectamin (Revolution) applied as spot-on treatments once a month. All four of these active ingredients take 24 to 48 hours to be effective, and each offers slightly different benefits.

• Imidacloprid kills adult fleas and has a month-long effect.
• Fipronil also kills adult fleas for a month as well as ticks.
• Selamectin protects for a month against a host of pests including fleas, ear mites, heartworms and certain types of ticks.
• Nitenpyram, taken as a pill, kills adult fleas that feed on a treated pet within 20 minutes but is only effective for 24 hours and isn’t helpful for flea-allergic animals.

Some of the most effective flea and tick products today combine an adulticide to kill adult fleas with an IGR to control the immature bug population. You can find a fipronil and methoprene combination product that kills fleas and ticks (Frontline Plus), as well as etofenprox partnered with Nylar or methoprene in various over-the-counter spot-on products that help control fleas and ticks. Products that contain imidacloprid with permethrin (K-9 Advantix, for dogs only) or spinosad (Comfortis for dogs) also are available.