With a single female flea capable of laying thousands of eggs in her lifetime, a small flea problem can quickly become an infestation. Experts say the only truly effective way to keep fleas off a dog or cat is with a topical or oral medication. Flea shampoo, dips and sprays only provide immediate relief by killing adult fleas on the pet. They won't prevent the dog or cat from picking up more fleas from around your home or eggs that hatch. Although many topical and oral flea-control products are available online without a prescription, always consult your vet before purchasing one. It is important to choose the right dosage and to avoid harmful interactions with other medications your pet may be taking.

Veterinarians recommend using topical flea treatments during peak flea season (when warm weather sets in) or to resolve an existing flea problem. Oral medications may be a better choice for permanent flea control, which is often necessary in warmer climates. Oral medications also have a lower risk around pregnant women, children and other pets, because there's no chance of contact with chemicals during or after application as with topical flea treatments.

The primary difference between various methods of topical and oral flea control is the active ingredient. The product may contain a pesticide that kills adult fleas and/or an insect growth regulator (IGR) that breaks the life cycle by preventing flea eggs from hatching and larvae from pupating into adults. Some products provide additional benefits, such as preventing heartworms, ticks and other parasites. Another key buying consideration when treating a puppy or kitten is comparing the minimum age requirements.

Experts give the following advice for safely using flea control topical treatments and oral medications:

  • Talk to your vet before purchasing a flea control treatment. Your vet may have specific recommendations for products he or she feels are most appropriate. This is especially important in the case of pets that are weak, older, medicated, sick, pregnant or nursing, or that have previously experienced an adverse reaction to a flea control treatment. Additionally, some products are not suitable for puppies and kittens.
  • Know your pet's weight. All flea control treatments are packaged according to the pet's weight. Don't try to guess your pet's weight or buy the wrong dosage because it's cheaper.
  • Follow the application instructions implicitly. Even if you have used the product before, review the directions to make sure they haven't changed. Many reported illnesses in cats and dogs from flea control products are due to misuse.
  • Never use flea control treatments designed for dogs on your cat, or vice versa.  Permethrin, a pesticide found in some topical dog treatments, is likely to be lethal to cats.
  • Wear gloves while applying topical treatments. According to the National Pesticide Information Center (NPIC), human contact with these pesticides may cause irritation, itching, or paresthesia (a tingly, prickly sensation) at the site of contact. If the pesticide is accidentally ingested, more serious health effects may include sweating, nausea, vomiting, headache, stomach pain, dizziness, weakness and seizures. The NPIC has fact sheets available with more detailed symptoms of exposure or poisoning in animals and humans.
  • Keep pets and children away until topical flea control treatments dry. Topical pesticides should not be ingested, and dogs and cats may decide to lick each other's fur at the application site. Choose products that are safe for both cats and dogs in households that have both.
  • Monitor the pet for signs of an adverse reaction. Unusual reactions may include skin irritation or redness, loss of appetite, vomiting, diarrhea, excessive salivation, trembling, depression or seizures. If these symptoms appear, immediately bathe the dog or cat in mild soap and rise with large amounts of water (unless the label states otherwise). Contact your veterinarian about the incident.
  • Don't reapply monthly topical treatments sooner than 30 days, even if fleas re-emerge. Contact your vet for advice.

If you aren't using a topical or oral flea-control product with an IGR, your pet will likely become reinfested in a few weeks unless you take action around the home and yard. You can begin by vacuuming your carpet daily, and cleaning floors (including along baseboards) and furniture that your pet comes in contact with to remove eggs and larvae. Seal the vacuum bag in a trash bag and discard it in an outside trash can. Steam-cleaning floors and other surfaces is also an effective method of killing fleas and their eggs. If bedding cannot be vacuumed or steam cleaned, wash it in hot soapy water every week or two.

Another option is to apply chemicals to the environment. You can use sprays that contain methoprene indoors (this IGR breaks down too quickly in sunlight) or pyriproxifen outdoors. There are also flea control powders and sprays that kill adult fleas, which can be used on furniture, bedding and floor, as well as foggers for broader coverage of an entire room.

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