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Flea Bite Pet Allergies & What to be Aware of | VetDERM Clinic

Flea Bite Pet Allergies & What to be Aware of


Fleas are a well-known skin parasite that can affect the well-being of our furry companions. Depending on the geographic location, fleas may be a seasonal problem, a non-seasonal problem, or they may not be a problem at all. In the Vancouver and Victoria areas, fleas cause infestations, allergies, and discomfort to cats and dogs year-round while being a minimal concern for pets in Saskatoon and Winnipeg due to a short flea season.

The common flea that affects cats and dogs is the cat flea, Ctenocephalides felis (scientific name). Other fleas exist but the cat flea is the most common species causing parasite infestations in dogs and cats.

Did you know that pets can have flea bite hypersensitivity and can be allergic to flea bites? Numerous allergens have been identified in flea saliva, that can result in an abnormally high degree of itch and skin inflammation in individual pets after they have been bit by fleas and exposed to the salivary allergens.

Just as food allergies can arise at any age, a pet may develop a flea allergy at any age. Thus, if flea bite allergy is suspected in an itchy pet, knowing that your pet has not shown an allergy to fleas in the past is of minimal benefit.

Life Cycle of a Flea

The flea life cycle starts with the egg, followed by larval stages, pupa formation, and finally the adult stage. The flea life cycle is complex and depends on many factors such as temperature, humidity, season, availability of host animals to feed on, etc. The female flea lays her eggs on the host usually while the dog or cat rests or sleeps. Flea eggs fall from the host into the environment, where the life cycle is completed.

All life stages of the flea are sensitive to environmental conditions including temperature and humidity. Fleas love mild weather and especially thrive at temperatures between 20° and 30°C, with high reproductive rates (think high numbers of the parasites being produced!). Low temperatures of less than 0°C for 36 hours or longer are usually lethal to most flea eggs. This is one of the reasons why Vancouver and Victoria weather permits for year round flea bites and flea infestations in our pets.

Adult fleas need a host animal for long term survival. Once they do find an animal host adult fleas can survive for more than 100 days.

Symptoms and Effects of Flea Infestation

Non-allergic pets can harbour fleas with little or no discomfort. It is important to remember that these animals are at risk for a blood loss anemia due to blood loss from the feeding fleas over time. Female cat fleas will consume between 10 to 15 times their body weight per day. Aside from the blood loss and skin damage they cause, fleas can also carry tapeworms, and other organisms. Family members of pets infested by fleas are usually only bitten when too many fleas are present on a pet and they start looking for alternative feeding sources.

Around 70 female fleas can consume a total of 1 mL of blood per day. This is quite an amount of blood loss, especially for a cat or a small dog. And many more than 70 fleas may be present on a pet!

While flea infestations can be a seasonal problem (usually more of a problem during peak flea seasons of summer and fall), a pet can be affected by fleas during any season. Pets that are not allergic to flea bites will usually over-groom themselves or itch a little but don’t necessarily come across as uncomfortable pets. On the other hand, if a pet is allergic to flea bites, the signs would be no different from having pollen allergy or a food allergy i.e. symptoms will be more intense and obviously affecting the pet’s quality of life.

These symptoms include:

  • Frequent and severe itching and scratching (pruritus)
  • Paw licking
  • Over-grooming
  • Hair loss
  • Scabs

While there is no hard and fast rule about what signs a pet with a flea allergy may exhibit, the hind end and tail base areas of an animal are usually the most affected by itchiness, crusty lesions, and hair loss. If you see your cat or dog excessively licking, chewing, rubbing, or rolling, it’s best to get them checked by a veterinarian to help check for a possible flea allergy as well as other possible skin conditions.


Using a flea comb to inspect the hair can help to see the fleas and flea excreta easily. If evidence of fleas is noted, the diagnosis is easy. Some experienced pet owners may also easily diagnose this problem at home using a flea comb. However, evidence of fleas or flea dirt (flea feces that looks like dirt on the hair coat of a pet) may or may not be visible at first glance. In fact, it is often difficult to find evidence of fleas on a pet that is severely allergic to flea bites.

While the flea comb or a thorough hair exam can be helpful, this is not a method reliably used to rule out a flea allergy in an itchy pet. The best diagnostic, as well as preventative care, is to treat your pet for fleas.

When multiple pets live in the same house, and if all the pets are showing an increased itch, this can be quite suggestive of a flea problem. On the other hand, if only one pet is itchy while others seem quite comfortable, this does not rule out a flea infested home.

This is because only flea allergic pets will obviously be uncomfortable, while other pets may be getting flea bites without showing external signs. Think of people that are affected by mosquito bite allergy—it is not pleasant to get bit by a mosquito, but allergic individuals really react to mosquito bites while others scratch once and carry on with life! Fleas and flea bite allergies can work the same way in different individual pets.


If left untreated, your pet can develop a secondary bacterial or yeast infection of the skin from the inflammation created by flea bites as well as the trauma to skin related to itchiness. Antibiotics or antifungal treatments can be prescribed if your family veterinarian or vet dermatologist notes a secondary infection on your pet.

If needed, a short-term itch relief medication can also help with comfort. For long-term treatment and control, obtaining a diagnosis of flea infestation or a flea allergy is key for the well-being and comfort of your pet, as only a firm diagnosis will prevent further flea bite exposures.

Numerous flea prevention prescription products are available and most of them are quite safe for pets. Ideally these should be used to prevent a flea problem. If a flea infestation or a flea allergy situation does arise, these products are also used in treatment of fleas, along with good environmental control within the home environment.

Remember, a product that is safe for dogs may not be safe for cats as kitties can be more sensitive to certain products. Also, some products are not as effective as others. Always consult with a veterinarian before using a flea treatment to ensure safety and good efficacy.

Based on your pet’s life style, age, and general health, a safe flea treatment is usually easy to design. Flea control for all pets that spend any amount of time outdoors is highly recommended. A dog that only goes for short walks or a cat that only visits your yard for 5 minutes once in a while are also prone to picking up fleas from the outdoor environment. As Benjamin Franklin once famously said, “An ounce of prevention is worth a pound of cure”.

Creative Commons Attribution: Permission is granted to repost this article in its entirety with credit to VetDERM Clinic and a clickable link back to this page.




Dr. Jangi Bajwa is a Board certified veterinary dermatologist at VetDERM Clinic in Surrey BC. He is also the dermatology feature editor for Canadian Veterinary Journal. Dr. Bajwa’s special interests include otitis and allergic disease in pets; as well as helping improve quality of life of pets and their families.


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