Flea Infestation and Flea Prevention in Dogs


Fleas are parasitic insects: they live on the skin and eat the blood of their hosts. Fleas are found worldwide in temperate areas. Adult fleas live and feed on dogs and other animals, including humans. They excrete visible ‘flea dirt’ or feces. They jump easily from animal to animal and can bite within minutes of landing. Fleas present a public health risk to humans because they are the vector for a variety of infectious agents that cause diseases in humans. Dogs and other pets are one of the main sources of human flea exposure.

Dogs are at similar risk for infectious diseases, and consuming fleas during grooming exposes dogs to tapeworms. Fleas can consume enough blood to lead to anemia, especially on small or predisposed canine hosts. Flea saliva is the trigger for flea allergy dermatitis, the most common allergic skin disease of dogs.

 It is recommended that all dogs stay on a veterinarian-approved form of flea prevention year round. In addition to medical preventatives, it is important to check a dog’s skin regularly for signs of infestation. The sooner fleas are found (and treated), the less damage they do. Many dogs with fleas show no symptoms at all, but symptoms of flea infestation may include itching, scratching, rubbing, irritation, and restlessness. Adult fleas and flea dirt may be visible on the dog’s skin and coat.

A note about “natural” flea control products: an abundance of pesticide-free products claiming to kill, prevent, or repel fleas are available on the market. There are no natural products currently on the market backed by scientific evidence that supports their safety for use nor their efficacy in preventing or eliminating fleas.

Risk Factors

Fleas are ubiquitous in many environments, so failure to take preventative measures is likely to result in a large infestation that may take months to resolve. People and pets living in heavily infested environments may also need to employ a professional pest-elimination service to treat their homes and yards. Finding a flea on a dog is not an emergency, but it is an immediate call to action. Eliminating fleas once they are established is difficult, but prevention is easy. 

It is essential to break the flea life cycle entirely in order to successfully eliminate a flea infestation. This is because there are four stages of the flea life cycle and each stage bears some resistance to treatment.

The four stages are: eggs, larvae, pupae, and adults. Adult fleas lay up to 50 eggs a day in the host’s fur, which are then scattered wherever the animal stays regularly. Eggs hatch within 2 - 14 days and the emerging larvae are more likely to survive on protected surfaces like in carpet, upholstery, or bedding. 5-20 days later, the larvae spin a cocoon and pupate. In the pupal stage, fleas can live for up to one year while waiting for the right conditions; i.e. a host to feed from. Their thick cocoon provides protection against harsh environmental conditions like freezing, drying, and exposure to insecticides.  Once they emerge from the pupae, adult fleas hop onto a new host, feed, reproduce, and start laying eggs to begin the cycle again.

Possible Causes

A large scale flea infestation is caused by a lack of (or inadequate) preventative parasite control. Dogs may be exposed to fleas at any time, but it is not likely to develop into a larger problem if preventative measures are already in place.

Main Symptoms

Many dogs with fleas show no symptoms at all. The physical presence of fleas is easy to overlook, especially when the population is small. Dogs who are not allergic to flea saliva are unlikely to be itchy or develop a rash. The main symptoms of flea infestation in dogs are:

• Irritation - Scratching, licking, rubbing, or biting are often signs of flea infestation.

• Adult Fleas - visible confirmation of the presence of adult fleas.

• Flea dirt - Small black specks on the skin or in the bedding. To distinguish flea dirt from regular dirt, wet it - flea dirt (the blood of its host) turns reddish brown. Many pet parents discover their dog has a flea problem when they bathe the dog and see blood swirling in the water. 

• Rash - Dogs who are allergic to flea saliva develop a severely itchy rash characterized by loss of hair, red skin, and scabby sores. This rash is usually worse over the hips and near the base of the tail.

Detailed Characterization

If undetected, or if a dog has an underlying predisposition, flea infestation may also result in other generalized symptoms of flea-borne illness and/or anemia like lethargy, appetite loss, weakness, and coughing.

Testing and Diagnosis

Diagnosis of flea infestation is straightforward. The vet will physically examine the dog’s fur for evidence of fleas, but failure to find fleas does not rule out their presence. If secondary symptoms of flea-borne illness, anemia, tapeworms, or flea allergy dermatitis have developed, additional diagnostics may be necessary. Safe and effective pesticides are an important part of flea treatment and prevention. Choosing an effective and safe pesticide is difficult, so get professional advice from a veterinarian. Use all pesticides exactly as directed. Be aware that many flea control products available over-the-counter are unsafe, even when used as directed. Many are also ineffective. Your veterinarian is the best source of information to guide your flea control and prevention plan. 

Your veterinarian will choose from two basic categories of pesticides: 

• Oral prescriptions (these work best for most dogs)

• Topical products (either spot-ons on collars)

In order to successfully eliminate an existing flea population, the selected pesticides must be:   • Used on every pet in the household

• Correctly applied on time and administered exactly as directed

• Used for at least three months, and sometimes even longer

Once a flea infestation is confirmed, the challenge is killing all the eggs, larvae, and fleas in the dog’s environment (especially in its favorite places - beds, carpets, furniture), vehicles, or yard.  If indicated, your vet may also recommend environmental pesticide treatment, either with a proven safe and effective spray containing an insect growth regulator or by contracting a professional service. 

In the house, yard, and car, the goal is to break the life cycle by removing as many eggs, larvae, and pupae as possible.

• Vacuum floors, upholstery, and mattresses. Flea larvae thrive on protected substrates like carpet and away from high-traffic areas. Focus especially on these areas when cleaning. Dispose of the vacuum bag outside of the house so the fleas don’t just hop back onto the floor. 

• Wash all bedding where pets are allowed in hot water using detergent. Dry at the highest heat setting and repeat at least every two to three weeks.. If bedding is older and the infestation is serious, consider buying new bedding.

• Use appropriate premise sprays as recommended by the vet or pest professional.

Making your yard less inviting to wildlife and other animals can help minimize your dog’s exposure to fleas. 

• Install a solid fence

• Increase sunlight to the yard by trimming trees; eliminate as much shade as possible

• Mow the grass regularly, keep bushes cut short, and clear leaf litter and organic debris from under bushes and in flower beds.  Don’t put this waste in the compost pile. 

• Spread cedar chips where the dog lies regularly. Fleas don’t like the smell.

• Buy nematodes (small worms that eat insect larvae) from the local garden center and sprinkle in the lawn and other areas. 

• Don’t overwater the garden or lawn, as fleas thrive in humidity. 

• Regularly spray an approved insecticide in places where the dog spends time like dog houses, gardens, flower beds, and shady places like under porches and decks. Always use pesticide sprays as directed by your veterinarian.

• Keep the dog out of places wild animals with fleas might go like crawl spaces, cool hidden corners, and garbage storage areas.

• Discourage wildlife from investigating your property. Install bright lights, play loud music, put up barriers, and leave cider vinegar soaked rags around until they move on.

Steps to Recovery

Flea infestation will last as long as preventative treatment is not deployed. Once treatment has begun, it may take up to 3 months to fully break the flea life cycle and end the infestation.


Fleas can be transmitted between animals and from animals to people. They are prevented using a combination of preventative pesticide treatment and environmental controls.

Is Flea Infestation Common in dogs?

Fleas are the most common known ectoparasite reported in dogs

Typical Treatment

Preventative pesticide, environmental controls

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