Fleas in Dogs

Causes, Treatment, and Prevention

Dog scratching fleas

Carol Yepes / Getty Images

Fleas make dogs miserable with itching, but they can also cause allergies and anemia. They can even transmit tapeworms to their hosts. These parasites can be tough to eradicate when they invade your home, so prompt and aggressive action is necessary. All of the pets in your household will need treatment, and your furnishings may require deep cleaning as well.

What Are Fleas?

Fleas are flightless external parasites of both birds and mammals. Adults are about three millimeters long, with flat bodies and strong claws that cling to a host's skin, fur, or feathers. Fleas have mouth parts that allow them to pierce the skin and drink blood. Adult fleas represent only five percent of the total flea population; the remaining 95 percent, composed of flea eggs, larvae, and pupae, lurk in the surrounding environment.

Symptoms of Fleas in Dogs

Dogs cannot have fleas for very long without their owners noticing. Symptoms of early infestation are less severe than those of a prolonged problem.


  • Itching (scratching or biting skin)
  • Particular itchiness near the base of the tail
  • Fleas visible in fur
  • Black flecks in fur

Dogs with fleas are usually quite itchy. Fleas prefer the back end of dogs, causing your pet to chew at its flanks and above its tail region. Flea bites can also cause skin swelling, irritation, ulceration, and hair loss.

If you part your pet's coat you might see flea feces ("flea dirt"), which looks like tiny black specks. You may also see live fleas scurrying through the hair.

Pets with flea allergies have severe itching in response to a single flea bite. These pups are allergic to the saliva from the flea.

illustration of signs your dog has fleas
The Spruce / Kelly Leigh Miller

Causes of Fleas

Fleas can lay 20 to 40 eggs per day, and it only takes 10 female fleas to create almost 250,000 different life stages in a single month. Newly emerged flea larvae can survive two weeks without a blood meal, and pre-emerged fleas (pupae/cocoon stage) can survive six months without feeding.

Generally, dogs contract fleas outdoors, but they can also pick them up from other infested dogs or cats. Certain environmental factors may increase the odds of a dog attracting fleas, including:

  • Moist, wooded surroundings or long grass
  • Flea-infested boarding facilities or dog parks
  • Indoor flea infestation (carpets, bedding)
  • Neighboring flea problems (especially in apartment complexes)

Diagnosing Fleas in Dogs

Most owners and veterinarians can easily recognize fleas on sight. Even in a dog with few fleas, you can generally find evidence of their presence—if not adult fleas, the specks of flea excrement. When looking for flea signs, check the area around the base of the dog's tail with extra care. The hair in this area is often dense and hides fleas well. Fleas gravitate to dogs' rear regions because of the dense coat and the fact that dogs can't reach them easily with their teeth or claws when scratching.


Treating fleas involves removing and killing existing adult and juvenile fleas. Flea products address the egg, larval, and adult stages, but no insecticide kills the cocoon (pupal) stage. Until all the immature fleas have hatched out of the pupae in their environment, you will continue to see fleas, therefore you must continue treatment throughout the fleas' 21-day lifecycle to achieve full eradication.

Non-Chemical Methods

Many pet owners seek non-chemical flea control methods. The safest and most “natural” flea control technique involves using a flea comb to manually remove fleas, eggs, and flea dirt. This method is only practical with low levels of flea infestation.

Frequent vacuuming of the carpet removes up to 90 percent of flea eggs and 50 percent of larvae. You must also wash pet beds, carriers, blankets, and throw rugs as well as any sofa cushions or other favorite pet resting places.

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 young dogs.

Insect Growth Regulators (IGRs)

While the above-mentioned options can help reduce flea populations, 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 pets and are one of the safest flea ingredients. For example, 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 ingredients that specifically attack the flea's nervous system. These include imidacloprid (Advantage), fipronil (Frontline), selamectin (Revolution), and nitenpyram (Capstar.) These are applied as spot-on treatments once a month. Each of these four active ingredients takes 24 to 48 hours to be fully 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.

Adulticides with IGRs

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 pyriproxyfen (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.

Prognosis for Dogs with Fleas

A heavy flea infestation or one involving multiple pets can be a challenge to control. These situations require a diligent, multifaceted approach that targets all household pets (mammals and birds) and sanitizes the home environment. After a three-week treatment regimen, though, dogs can resume life without the discomfort of fleas. Puppies that suffered from anemia will require a bit more support and possibly nutritional supplementation to regain health and start growing with vigor.

How to Prevent Fleas

Fleas hate direct sunlight and prefer outdoor shaded areas with sand, leaves, or other debris. So, in part, the lifestyle of your dogs determines their risk for exposure. Indoor couch potato pups probably don't need the same protection as hunting dogs that roam in the field. But even dogs that visit the yard on a leash have enough exposure to warrant flea protection in some places.

Keeping your lawn cut short will ensure sunlight exposure. Most parasites find this an unappealing environment. Keeping pets away from problem areas and treating the bug habitats helps reduce the pest population. Nematodes—worms that eat immature fleas—are available from lawn and garden supply outlets.

While parasites are most active during warmer months and they are susceptible to extreme cold, it's hard to predict when fleas are most likely to be a problem. Thus, the Companion Animal Parasite Council (CAPC) recommends year-round protection against fleas and ticks.

Consult with your veterinarian about how to best protect your dog in the battle against fleas. The most effective products are available only by prescription. If you choose an over-the-counter product, examine the label carefully and strictly follow product instructions to ensure the health and safety of your pets.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.

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Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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