FLEA ALLERGY Part 1: 3 Scary Flea Facts You Might not Know

Flea allergy is one of the most common causes of itching in dogs!  Flea allergy dermatitis occurs when dogs develop sensitivity the bite of fleas. Interestingly, dogs and cats that are not allergic to flea bites develop lesions or itching from the bites.  So… contrary to popular belief not all dogs with fleas itch!



1.    Fleas are known for their biting and blood-sucking abilities.

Fleas are wingless, external parasites found on dogs and other pets (cats, rabbits, guinea pigs and ferrets) and wildlife (raccoons, opossums, deer, cattle, coyotes, foxes, bobcats, and skunks). The most common species of flea that affects dogs and cats is known as the “cat flea” (Ctenocephalides felis). However, don't get confused by the name; it's called the cat flea, but it is the number one flea of all pets, dogs included.

2.    Despite advances in flea control, flea bite allergies and flea bite dermatitis still continue to be common problems.


Dogs that are prone to developing allergies begin to show symptoms once they have become “sensitized” to the flea’s saliva encountered when the flea bites. Studies have shown that there are over 15 different antigens in the saliva of the flea! Each one of these is capable of causing an allergic response in a sensitive dog or cat.


What are the symptoms of flea allergy?

Flea bite allergy (“Flea allergy”, “Flea allergy dermatitis”) is worse during peak flea times. Therefore, symptoms are seasonal in temperate areas (warm weather through fall) and nonseasonal in subtropical or tropical areas. Believe it or not... in some areas fall can be the most severe season. When that first cold snap occurs it seems to awaken some of those fleas! Of course, if there is an infestation in your home there can be no seasonal pattern at all.


3.    Finding fleas or flea dirt (feces) can confirm suspicions but in many cases fleas are not present. So lack of fleas does not mean your dog does not have flea allergy!

Dogs with flea allergy will bite at the base of their tail and scratch frequently. They will often exhibit a “corn-cob” chewing behavior along their rump or front legs. Even bites from a few fleas can cause hours and days of intense itching. Many dogs have a characteristic loss or thinning of hair above the base of the tail. Finding fleas or flea dirt (feces) can confirm suspicions in many cases but are not present all of the time. If a dog is bathed or treated regularly, there can be very little evidence of fleas on your dog. Here’s a trick… to tell if you are dealing with flea dirt, you can perform a simple test. The flea dirt will dissolve into a red color when moistened; this is because it is primarily digested blood. Severely affected dogs may itch over their entire bodies, have generalized hair loss, and red inflamed skin. Hot spots are often a result of flea bite allergies.


The treatment for flea allergy involves strict flea prevention and control of fleas within the environment- we will cover more of this in Part 2 of this blog.  Some studies have shown that up to 40% of dogs in any given area will test positive for flea bite allergies with symptoms developing at any age.


The Flea Life Cycle and Your Environment

Fleas are often hard to see as they dash out of sight! Have you ever tried to catch one on your dog? Fleas are tiny and look like copper or black pepper flakes. Importantly, when you do see a flea, know that a dozen of their comrades are around and in hiding. Flea eggs are microscopic and fall off pets and to the floor, usually resting in cracks between boards, along moldings, or in leaf litter. Even though adult fleas can be easily killed, it is usually the flea eggs that are the major problem, because they are harder to find and have a hard exterior shell protecting them. The flea life cycle can be completed in 2 weeks with new eggs hatching every 10-14 days.

The majority (95%) of the flea population exists in carpet and grass. To properly control a flea infestation you should use pet flea control products and remove fleas in the surrounding environment by using a home flea treatment. And if your pet spends any time outdoors, make sure you thoroughly use flea yard spray. 

A Quick Review

How do I know if my dog has flea allergy? I am NOT seeing fleas!

·      Location, location location…. Flea allergy causes itching and dermatitis (hair loss, redness, scaling) along the rump, tail, thighs & belly. A “corn cob”-chewing pattern along the front legs can also be seen.

·      Visualization of fleas or flea excrement (“flea dirt”) is helpful but not required for a diagnosis.

·      Allergy testing (intradermal, serologic) should show a positive reaction to flea, but false negative results do occur.

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