Cat allergies most often manifest as itching and skin changes. The cat may lick or scratch so much that the fur disappears, develop small crusts on the skin or sores around the head and neck. Flea bites, food and environmental allergens can be triggers – but several other conditions cause almost identical symptoms, which is why the investigation is so important.
How does allergy manifest itself in cats?
Cats react in some fairly recognizable patterns. A cat may have one of them, or several at the same time.
- Self-inflicted hair loss – the cat licks itself bare, often symmetrically on the stomach, inner thighs or flanks. The skin underneath may look completely normal
- Miliary dermatitis – many small crusts that feel like grit in the fur, often along the back and neck
- Itching around the head and neck – the cat scratches itself, often to the point of wounds and scabs
- Eosinophilic skin changes – raised, red patches on the abdomen or thighs, swollen areas on the chin, or a sore on the upper lip that does not heal
- Ear problems – recurring ear infection in some cats
- Stomach and intestinal symptoms vomiting or diarrhea, especially in feed reactions
Cats often groom themselves in secret. Many owners don't notice the hair loss until the vet turns the cat over and finds the bare belly.
Coughing or difficulty breathing is something else. A cat that is breathing heavily, sitting with a straight neck or an open mouth needs to be evaluated quickly. It could be asthma or other respiratory or heart disease, and should not be considered an "allergy". Read more about emergency care at A-Vet.
Other causes may resemble allergies
A cat licking its bare belly or inner thighs does not necessarily have an allergy. Cats may groom a painful area more than normal, and among other things urinary tract problems, abdominal or joint pain and stress can cause similar behavior.
Additionally, parasites, skin infections with bacteria or yeast, and some fungal infections can cause similar itching. This is one reason why the diagnosis is not made on appearance alone.
Common causes of allergic skin disease in cats
Environmental allergies
Cats can react to pollen, dust mites, mold, and other allergens in their environment. Exposure doesn't just happen through inhalation – the skin is also an important contact surface.
Some cats have seasonal variation, while others have problems all year round. Environmental allergies are a key differential diagnosis for persistent itching in cats, but it is only made when other causes have been considered.
Food allergy
Food reaction is an important differential diagnosis in cats with persistent itching and skin changes. It can occur suddenly, even to food the cat has eaten for years.
Allergies develop to proteins the cat has been previously exposed to, and it is not possible to determine the cause just by reading the ingredient list. The itching is usually around the head and neck or on the underside of the body, and some cats also have stomach and intestinal symptoms.
Flea allergy
Flea allergy is a reaction to proteins in flea saliva. In a cat that has first become allergic, getting flea bites causes severe symptoms – and because cats groom themselves thoroughly, you often find neither fleas nor flea dirt in their fur.
That's why flea control is usually the first step in the investigation of an itchy cat, even when the owner is sure the cat does not have fleas. Read more about fleas in cats.
Never use flea or tick medication intended for dogs on cats without express advice from a veterinarian. Some active ingredients in dog products are highly toxic to cats and can cause life-threatening poisoning. Treatment and prevention should be done with a parasite control product that is approved for cats.
Contact reactions to substances or products the cat comes into contact with can also occur, but are far less common than the three above.
How are allergies diagnosed in cats?
Cat allergies are a diagnosis of exclusion. They are made by assessing the patient's medical history and skin changes and systematically ruling out other causes of itching. The investigation usually proceeds in this order:
- clinical examination of skin, fur and ears
- parasite control – fleas and other mites are assessed and treated
- samples from the skin under a microscope, to look for bacteria, yeast, and parasites
- assessment of fungal infection where applicable
- elimination diet if food reaction is suspected
- environmental allergies are considered last, once the rest has been clarified
Elimination diet
If a food allergy is suspected, a strict elimination diet is implemented, usually with hydrolyzed protein or a carefully selected protein source that the cat has not previously received. The diet usually lasts eight to twelve weeks.
The cat should only eat the diet that has been chosen together with the veterinarian. Treats, leftovers, other cat food, flavored medications, and prey can invalidate the test, making a reliable elimination diet difficult for an outdoor cat who hunts.
To confirm a food reaction, previous food is reintroduced under controlled conditions. If symptoms return, this significantly strengthens the diagnosis.
Is there an allergy test?
There is no blood test that can diagnose environmental allergies in cats alone. Blood or intradermal allergy testing is primarily used to identify relevant allergens when allergen-specific immunotherapy is being considered, after other causes of itching have been ruled out.
Healthy cats can respond to such tests. A positive result does not in itself mean that the cat is sick from the allergen in question.
How are allergies in cats treated?
Treatment is tailored to the cause and may include control of triggering factors, treatment of secondary skin or ear infections, anti-itch treatment, and in some cats, allergen-specific immunotherapy.
Secondary infections are an important part of the picture. The cat is itching because it is allergic, but the skin often becomes infected from the scratching – and then it itches even more. Both parts need to be treated in order for the cat to rest.
Do not use leftover allergy medications, skin creams, or parasite control products without first checking with your veterinarian. Several preparations intended for humans or dogs are unsuitable or toxic for cats.
Many allergic diseases in cats require long-term follow-up, but treatment and prognosis depend on what triggers the reaction. A food reaction is managed with permanent avoidance, flea allergy with flea control, while environmental allergies usually need to be followed up over time.
When should a veterinarian be contacted?
Contact your vet if your cat is persistently itching, losing fur, developing sores or scabs, or has recurring ear problems. The same applies to persistent vomiting or diarrhea.
Contact us immediately if the cat is breathing heavily or has difficulty breathing.
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If you also have a dog, you will find similar information on the page about allergy in dog.
