• Flea allergy dermatitis (FAD) is a severe allergic reaction to the bite of a flea.
  • FAD can cause intense itching and painful skin wounds.
  • Left untreated, affected animals can develop secondary skin infections.
  • FAD can be treated by controlling fleas on the pet and removing fleas from the pet’s environment.
  • Corticosteroids and antibiotics may be prescribed to treat itching and secondary skin infections.

What Is Flea Allergy Dermatitis?

Flea allergy dermatitis (FAD) is a severe allergic reaction to a flea bite. Both dogs and cats can develop FAD. Affected pets have an extreme allergic reaction to certain proteins in the flea’s saliva, which the flea injects into the pet’s skin during biting and feeding. Some pets are so allergic that even a single bite can cause a reaction.

FAD makes pets feel miserable, and if left untreated, the associated severe itching and inflammation can lead to excessive scratching and chewing that can damage the skin. Secondary bacterial or fungal infections can develop as a result.

What Are the Signs of Flea Allergy Dermatitis?

Discomfort and itching are among the first signs of FAD. FAD can be more severe during warm/humid weather, when fleas are more active. However, if a pet’s home environment is infested with fleas or the pet lives in a place that is warm year-round, FAD can be a chronic, year-round problem.

Affected animals may scratch, bite, lick, and chew excessively at itchy and inflamed areas. Red, oozing lesions called hot spots may develop in areas where the scratching is most intense—typically on the rump, tail, and legs. Affected dogs typically exhibit thinning of the hair along the rump and the base of the tail. Affected cats can remove large areas of hair and develop scabs that can cover most of their body.

Other signs include:

  • Skin inflammation
  • Hair loss
  • Scabs
  • Oozing or crusted sores (hot spots)
  • Darkening or thickening of affected skin
  • Unpleasant odor (resulting from secondary infection)

Diagnosis of Flea Allergy Dermatitis

Diagnosis is typically made through examination and on finding evidence of fleas. However, because a single bite can cause a reaction and because many pets, particularly cats, can do an excellent job of grooming fleas off of themselves, evidence of fleas may not be found. Allergy testing can help determine whether the pet has a sensitivity to flea saliva. Because pets that are allergic to fleas are often allergic to other substances, additional allergens may be tested for as well.

Treatment and Prevention

The only truly effective way to treat FAD is to completely prevent flea bites by removing fleas from your pet and its environment. Effective treatment targets adult (biting) fleas, but many products also target the other life stages of fleas (such as eggs and larvae), which can live in the environment and mature into adult fleas.

There are many safe, effective, and easy-to-administer flea-control products. These products are typically administered by applying the medication as a fluid directly to the animal’s skin—generally between the shoulder blades or at the back of the neck. Your veterinarian may recommend more than one product to most effectively kill fleas and break the flea life cycle.

Once an infestation is established in your home, fleas can be very difficult to eliminate. You may need to treat your pet repeatedly. In addition, fleas must be completely removed from the affected pet’s environment. Therefore, all other animals in the house must also be treated with flea-control products, and the house (and possibly the yard) may need to be treated with flea-control products as well.

Vacuuming rugs, throwing out old pet bedding, and laundering other items may also be recommended by your veterinarian to help remove fleas from your pet’s environment. Because many species of wildlife carry fleas, it may also be recommended that you secure your home and yard to prevent wildlife from inadvertently re-infesting your pet’s living and exercise areas.

Secondary skin infections that develop as a result of FAD may be treated with antibiotic or antifungal medications. In addition, your veterinarian may prescribe a short course of corticosteroids to reduce inflammation and itching so that irritated areas may heal.

There are more than 2000 species of fleas, but the one that most commonly afflicts dogs and cats is the cat flea (Ctenocephalides felis).