Moderate severity

Mosquito-Bite Hypersensitivity

An allergic skin reaction to mosquito bites, causing crusty sores and hair loss on the thinly haired bridge of the nose and the ear tips.

⚠️ Common symptoms

Crusts, bumps and sores on the bridge of the nose and ear tipsHair loss and scabbing in these thinly haired areasRedness, swelling and itchiness of the affected skinSometimes small ulcers or oozing where bites clusterSigns that worsen in warm weather and improve indoors

Mosquito-bite hypersensitivity is an allergic skin disease seen in cats that spend time outdoors or near open windows in mosquito season. Rather than a general itch, it produces a distinctive pattern of crusting, bumps and hair loss on the least-protected skin — the bridge of the nose and the tips of the ears — because these thinly furred areas are where mosquitoes most easily reach.

The reaction is driven by an over-sensitive immune response to proteins in mosquito saliva. In a sensitised cat, each bite provokes inflammation, and repeated bites over a warm season can leave the nose and ears looking sore, scabbed and patchy. The affected skin is often itchy and may become swollen, and clusters of bites can develop into small ulcers.

Because the crusty, hairless appearance can mimic ringworm, sunburn-related skin cancer or immune-mediated disease, a veterinary diagnosis is important. Reassuringly, the condition typically responds well once biting is prevented and the inflammation is treated, and it tends to be seasonal, easing as mosquito numbers fall. The key long-term strategy is bite prevention, using only cat-safe products, since dog insecticides containing permethrin can be fatal to cats.

🔍 Causes

The condition is a hypersensitivity, or allergic, reaction to the saliva injected when a mosquito bites. The sparsely furred skin of the nose and ears is most exposed, so this is where the reaction concentrates. Repeated bites in sensitised cats trigger increasingly obvious inflammation.

🛡 Prevention

Reduce exposure by keeping susceptible cats indoors during peak mosquito hours, using screens on windows and doors, and removing standing water where mosquitoes breed. Only ever use insect-repellent products specifically labelled as safe for cats, and check with your vet first.

💊 Treatment

The mainstay of treatment is preventing further bites by keeping the cat indoors at dawn and dusk when mosquitoes are most active. A vet may prescribe anti-inflammatory medication such as a short course of steroids to calm the allergic reaction, along with treatment for any secondary skin infection. Cat-safe insect control around the home helps, but never use dog mosquito or flea products, as many contain permethrin, which is highly toxic to cats.

When to see a vet: See a vet if crusty sores, hair loss or persistent scabs develop on the nose or ear tips, particularly in warmer months. Prompt treatment settles the inflammation and rules out other look-alike conditions such as ringworm, skin cancer or autoimmune disease.

⚕️ Medical disclaimer

  • This information is educational only and is not a substitute for veterinary advice.
  • Symptoms overlap between conditions — only a vet can diagnose accurately.
  • Never withhold treatment or self-medicate based on information found online.
  • When in doubt, call your vet. Early intervention almost always leads to better outcomes.

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