Middlesex Veterinary Center

Flea Allergy in Cats

Cats are known for their cleanliness and grooming habits, but even the most well-groomed feline can suffer from skin allergies. One of the most common causes of skin allergies in cats is flea allergy dermatitis, a reaction to the saliva of fleas.

What Are Allergies, And How Do They Affect Cats?

One of the most common conditions affecting cats is allergy. In the allergic state, the cat's immune system "overreacts" to foreign substances (allergens or antigens) to which it is exposed. These overreactions are manifested in several ways. The most common is itching of the skin, either localized (one area) or generalized (all over the cat). Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing. Sometimes, there may be an associated nasal or ocular (eye) discharge. The third manifestation involves the digestive system, resulting in vomiting or diarrhea. The specific response that occurs is related to the type of allergy present.

Does that mean that there several types of allergies?

There are five known types of allergies in the cat: contact, flea, food, bacterial, and inhalant. Each of these has some common expressions in cats, and each has some unique features.

What is meant by the term flea allergy?

In spite of common belief, a normal cat experiences only minor skin irritation in response to flea bites. Even in the presence of dozens of fleas, there will be very little itching. On the other hand, the flea allergic cat has a severe, itch-producing reaction to flea bites. This occurs because the cat develops an allergic response to the flea's saliva. When the cat is bitten, flea saliva is deposited in the skin. Just one bite causes intense itching.

What does this reaction do to the cat?

The cat’s response to the intense itching is to chew, lick, or scratch. This causes hair loss and can lead to open sores or scabs on the skin, allowing a secondary bacterial infection to begin. The area most commonly involved is over the rump (just in front of the tail). This is probably because fleas find this part of the cat more desirable. Many flea-allergic cats also chew or lick the hair off of their legs.

What is the proper treatment?

The most important treatment for flea allergy is to get the cat away from all fleas. Therefore, strict flea control is the backbone of successful treatment. There are many products available for flea control, and many work in an entirely different manner. In some cases, multiple products may be needed. Some are used on the cat and some in the cat’s environment. Unfortunately, complete flea control is not always possible for cats that live outdoors in warm and humid climates, where a new population of fleas can hatch out every 14-21 days.

Some cats can be desensitized to the adverse effects of flea bites. Flea saliva extract (flea antigen) is injected into the cat in tiny amounts over a prolonged period of time. This is an attempt to reprogram the cat’s immune system so it no longer over-reacts to flea bites. If successful, itching no longer occurs or is less intense when the cat is bitten. However, this approach is only successful about 50-75% of the time.

When strict flea control is not possible, corticosteroids (or "cortisone" or "steroids") can be used to block the allergic reaction and give relief. This is often a necessary part of dealing with flea allergy. Some cats respond best to long-acting injections and others to oral medication. Cats are much more resistant to the side-effects of steroids than humans, but significant side-effects can occur if they are not used properly. For this reason, the goal is to administer the smallest amount of steroid needed to keep the cat comfortable. Some cats develop a secondary bacterial infection in the skin. When this occurs, appropriate antibiotics must be used.


Those instructions which are specific for your cat have been checked.

  1. An injection of steroids was given. Relief should be apparent within 12-24 hours. If not, please call. Your cat should feel better and itch less for about one month. It is important that you immediately institute appropriate measures of strict flea control. If an increase in water consumption or urination occurs, please report this to us for future reference. These side-effects are common with steroid administration and will go away in a few days without treatment. They may be avoided in the future by giving a lower dose. Return for further evaluation when the first signs of itching recur.
  2. Begin oral steroids when the first signs of itching return. Give ---- tablets every other morning. Adjust the dosage upward or downward to the lowest effective dose, with a maximum dose of ---- permitted. Stop giving the medication every 4-6 months to see if there are times of the year when therapy is not needed. Report any increase in water consumption to us at once.
  3. We have dispensed oral steroid tablets. Prednisone is most commonly used. The specific drug being dispensed for your cat is labeled on the bottle. Give ---- of the ---- mg tablets every other day for 3 doses (6 days), then ---- tablets every other day for 3 more doses (6 more days). Continue this downward progression ( ---- ) until the first signs of itching recur. At that time, go back to the next higher level and report that level to us (so we can be sure it is a safe level). Stop giving the tablets every 4-6 months to see if there are periods of the year when they are not necessary. When itching returns, begin immediately at the maintenance dose. If that does not stop the itching, increase the dosage slightly (to a maximum of ---- tablets) for a few doses, then return to the lower dose. Report any increase in water consumption to us at once. (This may occur at the initial dose but should stop on the maintenance dose.)
  4. Flea control is very important and should include treating the cat and its environment. The following products are recommended for your situation: ---- Bear in mind that flea allergy often accompanies other types of allergy, especially inhalant allergy. If your cat itches when fleas have been eliminated, notify us of that so that we can modify the treatment approach.
  5. Your cat has a bacterial skin infection secondary to its flea allergy. The following are recommended: a.) Antibiotics are to be used for the next ---- days. If the infection is not gone by the time the medication is completed, call for a refill or for a change in medication. b.) The medicated shampoo, ---- , is to be used every ---- days. Allow theshampoo to stay in the haircoat for a few minutes before thoroughly rinsing the cat. c.) The topical medication, ---- , is to be used ---- times daily for ---- days.

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