A complete guide to flea allergy dermatitis (FAD) in dogs

Flea allergy dermatitis (FAD) is caused by hypersensitivity to antigenic material from the salivary glands of fleas. Adult fleas require a “blood meal” in order to reproduce. They don’t usually remain on the dog except when they’re feeding and they inject a small amount of saliva into the skin. Proteins in the saliva cause an itchy response to sensitive dogs. A dog with FAD may suffer from just a few flea bites or even a single bite!

Fleas are tiny parasites that feast off your dog’s blood causing them to itch uncontrollably. Fleas jump from host to host! The life cycle of the flea is fairly straightforward.

• For every adult flea on the host there are a lot of eggs
• The life cycle is typically 3-4 weeks but may be shorter depending on environmental conditions
• Within 24 to 36 hours after the first blood meal, the female flea starts producing eggs
• These eggs are laid on the pet and also drop off into the environment

👉 Adult female flea can lay up to 40 flea eggs per day.

The top signs of flea allergy dermatitis are itching, licking, and intense biting of the skin. According to experts at Merck Vet Manual, “In dogs, the pruritus associated with FAD can be intense and may manifest over the entire body.”

• Small, raised lesions on the lower back, tail, head, and inner thighs
• Obvious restless and uncomfortable behavior
• Scratching, licking, rubbing, chewing, and even nibbling at the skin
• Hair may be stained brown from the licking
• Sores or scabs and crusty, oozy skin
• Presence of fleas or ‘flea dirt” (a combination of blood meal and flea poop!) on the skin
• Unpleasant odor
• Hair loss

Common areas on the body where there are lesions

Generally, the areas affected include the rump and tail, hind legs as well as areas of the head. Pet owners will also see itching and hair loss in the region from the middle of the back to the tail and down the rear legs (also known as the “flea triangle”). Some dogs may even have visible bite marks on their skin.

👉 As animals get older, the clinical signs of FAD tend to worsen and persist longer 

The visualization of fleas and flea dirt on an infested pet is helpful in a vet’s diagnosis. Veterinarians will also consider an intradermal test (ELISA) and skin biopsy. The dog’s age is also important because FAD doesn’t ordinarily occur in dogs before one year of age.

Fleas are becoming resistant to topical flea and tick preventatives, such as Frontline, Advantix, Effitix, and others that typically make the short-list. Therefore using a topical flea/tick product is no longer recommended by vets.

👉 Flea shampoos aren’t effective for treating fleas on your pet.

The most effective way to quickly treat fleas is by giving your dog an oral flea prevention (like Comfortis) or an oral flea/tick prevention (Bravecto, Credelio, Nexgard, or Simparica) year-round. These products are very effective in treating the entire life cycle of the flea and tend to kill all of the adult fleas within a few hours of administration. Vets recommend the following combination of oral preventives for dogs and one topical for dogs with food allergies:

• Sentinel Spectrum and Simparica monthly year-round — This combination protects your dog against heartworms, roundworms, hookworms, whipworms, tapeworms, fleas, and ticks. Simparica also has the fastest flea/tick kill compared with other flea/tick preventatives.
• Simparica Trio is multifaceted — Is an oral monthly preventative that protects against heartworms, fleas, ticks, roundworms, and hookworms.
• Trifexis is an oral monthly preventative — This medication protects against heartworms, fleas, hookworms, roundworms, and whipworms. There is no tick prevention with this product.
• For dogs with food allergies use Revolution — This topical is the safest option to use as it is a topical that is applied monthly for the prevention of fleas, heartworms, roundworms, and hookworms. (This topical is an exception because of the food allergy issue).

All oral medications require a prescription. Sentinel Spectrum is a heartworm and intestinal parasite preventative and Simparica is an oral flea/tick preventative.

These are available in a size that can be given to small dogs too. Sentinel Spectrum also has a size available for dogs weighing from 2–8 lbs. Customers on Chewy.com give this medication 4.2 out of 5 stars.

Ingredients: 23 mg milbemycin oxime, 460 mg lufenuron and 228 mg praziquantel.

This chewable tablet will protect your pet for a full 35 days and it also kills fleas before they lay eggs. Given the flea life cycle it is very important every adult dog is on a monthly flea control prevention medication and pet owners on Chewy.com give this option 4.6 out of 5 stars.

Ingredients: 80 mg sarolaner, hydrolyzed soy protein, starch, corn, wheat germ, anhydrous dibasic calcium phosphate, corn syrup, gelatin.

👉 Whenever you give something new to your dog, watch them closely for 24-48 hours. Call your vet if you notice any hives, vomiting, or diarrhea.

The most important tip for pet owners is to give your dog a monthly flea control medication. For any dog that suffers from FAD (or any/all dogs), you want to prevent fleas from biting your dog! There are many effective long-term flea control medications that will prevent fleas from reproducing.

Once a flea infestation is eradicated, most pet owners stop administering flea products. Instead, all pet owners need to talk to their vet about a monthly flea control medication year-round.

👉 Also it’s important for all pets (dogs and cats) in the household to be on flea prevention. Talk to your vet about flea preventatives for cats as they are different from dogs. 

Long-term monthly treatments. Pet owners should have their vet prescribe a flea/tick prevention medication for their dog and also treat for itchiness with either Apoquel (oral medication) or Cytopoint (injection). Your vet can talk to you about the best monthly treatment for your dog.

Flea sprays to help with the environment. There are sprays to help eradicate fleas from bedding, the yard, and furniture. Pet owners can spray carpets and hardwood floors. Treating the areas of the yard your dog spends a lot of time in will also help eliminate fleas. Knockout spray is the best option to eliminate fleas from the environment. Also, it’s important to wash any bedding in the washing machine and vacuum the house thoroughly to eliminate as many flea eggs as possible.

Shampoos to soothe skin. An oatmeal shampoo can be used to help soothe the skin but shampoos are often not needed as long as the fleas are treated quickly with oral flea/tick prevention.

There are many health issues that cause dogs to itch. Our pruritus explainer shares other common causes including:

• Parasites
• Seasonal allergies
• Food allergies
• Skin infection
• Dry skin
• Irritants

Flea saliva can cause an intense allergic reaction in some dogs. Flea allergy dermatitis may cause inflammation, alopecia, crusts on the skin, papules, red, irritated, and extremely itchy skin. Vets will look for fleas or flea dirt on a dog’s skin when they examine the canine and determine if this parasite is the cause of the allergic response.

With this in mind, fleas are a year-round problem and your vet can recommend a monthly flea control medication to protect your doggie.