Mosquito Bite Sensitivity in Cats

This usually presents as sores, ulcers, scabs and hair loss on thin-furred areas such as the face, nose or earflaps.

Cats usually lick off topical ointments or lotions used to treat mosquito bites. By: evanblaser

When an insect bites, it injects saliva, causing local irritation. Some cats become sensitized, and an allergic reaction is the result. The allergy, in addition to the itchy nature of the bites, can set up nasty swelling and infection.

Mosquitoes tend to prevail in the summer months in warm climates and be most active at dawn and dusk.

If your cat has mosquito bite sensitivity, then certain measures — such as keeping your cat indoors at certain times and mosquito control of the environment — can help keep the problem at a manageable level.



Mosquito bites usually occur on thin-furred areas such as the face, nose or earflaps.

An uncomplicated bite looks like a discreet raised scab, but cats tend to get more than one bite. A crop of itchy, scabby spots can become inflamed, and the cat then rubs her face and causes secondary bacterial infections. Severe cases can look quite dramatic, with sores, ulcers, scabs and hair loss covering the affected area.

Cats with the worst hypersensitivity reactions may be feverish with enlarged lymph nodes.


Mosquito bites, or the saliva that mosquitoes inject into the skin when the insect bites, are a potent source of allergens for cats.

These allergens trigger the body’s immune system to go into defense mode and try to get rid of the foreign substances. In a hypersensitivity reaction, the immune system overreacts, and the swelling around the bite site can cause more problems and be itchier than the original bite.

The first time a cat experiences a mosquito bite, a reaction is rare because the immune system has not yet been primed. It takes repeated exposure for a true hypersensitivity reaction to occur. The bad news, however, is that as time goes by with repeated exposure, the reaction can get worse and worse.


The importance of diagnosis with mosquito bite hypersensitivity is not so much to make a firm diagnosis but to make sure another condition is not being missed.


Skin complaints such as ringworm, cowpox and squamous cell carcinoma (a type of skin cancer that commonly affects noses and ears) look superficially similar to a hypersensitivity reaction and tend to be located in the same areas.

Not only do these other conditions show up on biopsies, but also hypersensitivity reactions are associated with large numbers of certain white cells called eosinophils. These eosinophils, while not specific to mosquito bites, are linked strongly to insect bites and allergic reactions.

Antihistamines tend to have disappointing results when used in cats with mosquito bites. By: zaimoku_woodpile


If the cat has severe skin lesions, she will need twofold treatment:

  1. A steroid for the underlying inflammation
  2. Antibiotics for the secondary infections

It is tempting to use ointments because they can do a nice job of acting locally on the skin, but cats tend to lick creams, rendering the medication ineffective.

Another disappointing treatment option is the use of antihistamines. Although this is the first option we would reach for if we had mosquito bites, their activity is underwhelming in cats and steroids are likely necessary. These may be used at a higher dose during a flare-up and a lower dose to prevent hypersenstitivity if the cat is determined to go outside during mosquito season.


Mosquito bites trigger hypersensitivity reactions, so avoiding exposure to mosquitoes is the best way to prevent this uncomfortable condition.

Mosquitoes tend to be most active at dawn and dusk, so a sensible precaution is to keep pets indoors at these times (or keep cats indoors at all times). Consider taking a look around the yard and local area and eradicating any standing water that may encourage mosquito populations.

Mosquito repellents (containing permethrin) are available, but they must be used with great care in cats because cats are extremely sensitive to the pyrethroids and there is a risk of overdose and toxicity. Cats who are particularly hypersensitive may need to take low doses of steroid during the mosquito season.


  • “Insect and arachnid hypersensitivity.” Bevier. Vet Clin North Am Small Anim Pract, 29(6), 1385–1405.


This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Dec. 17, 2018.