What are cat allergies or hypersensitivities?

Please note that, because cat allergies are such a broad subject, this article is a guiding overview. Follow the links in the text to go to the detailed articles about various forms of cat allergies, their diagnoses and treatments and how you can help your pet.

What are allergies?

An allergy, both in people and animals, is the condition when the immune system reacts to something completely harmless exactly as it would do when facing something harmful.

The immune reaction as a process is normal, but its target is completely wrong in its insignificance, a bit like shooting flies with a cannon. To highlight this reactivity to something that should be ignored, allergies are also often called hypersensitivities.

The things that can trigger allergic reactions are called allergens (allergy generators). The vast majority of allergens are proteins because these have large, unique shapes that are easy for the cells of the immune system to recognise and attack. Other types of substances can act as allergens if they attach to the body’s own proteins, changing their shape.

Sometimes, the name ‘hypersensitivity’ is incorrectly used for other reactions, like irritations or intolerances. The difference between a true allergic reaction and a non-allergic reaction with similar symptoms is that, with allergies, the immune cells produce and release antibodies that fit/attach to the allergen in a lock-and-key way. The concentration of these allergen-specific antibodies can be measured in the blood of allergic animals.

Same as with people, cats also inherit a predisposition to allergies from their parents.

It’s important to know that, in order to develop an allergy, an animal has to have had repeated contact with the allergens to build allergen-specific antibodies, they are not part of the ‘default’ immune arsenal.

Sometimes an allergy can lead to rapid symptoms (within minutes to hours) like hives or anaphylaxis but most often they result in slower reactions, gradually building up over longer periods of time (months to years).

How can you recognise if your cat has allergies?

Regardless of what triggers them, allergies tend to give very similar symptoms. Allergy-related sneezing, coughing, vomiting or diarrhoea can happen, but these are rare.

The main ‘allergy organ’ of the cat is the skin, which bears most of the symptoms.

An allergic flare-up in cats usually starts with an itch that can become very severe as the time passes. The itchiness can often go unobserved though because cats are fastidious groomers anyway and they often prefer to do this when alone.

Later you might see:

• skin redness, spots, weepy or crusty areas,

• patches of thinning coat or even complete baldness,

• thickening and darkening of the skin.

The body areas where these are seen differ slightly from allergy to allergy and are described in their respective articles.

Some cats also get:

• frequent ear infections,

• sores on their lips or body.

In the beginning, the skin symptoms are caused by the allergy’s damaging effect on the skin barrier but later they are made worse by the self-mutilation that the cats inflict on themselves by licking, scratching and nibbling their unbearably itchy skin.

The damaged skin gets secondary infections which add to the itchiness and pain and make the cat scratch more, which leads to more damage, then more itching, and so on in a vicious circle.

In severe cases of uncontrolled allergy, cats may become very depressed, eat less and lose weight.

What are cats usually allergic to?

The main allergies of cats are listed below, from the most common to the rarest. Some allergies can occur together.

1. Allergy to flea bites

All external parasites of cats can trigger allergic reactions with the allergens found in their saliva. The most common skin parasites of cats are fleas, therefore flea allergy dermatitis (FAD) is the most frequent form of parasite allergy in cats.

2. Food allergy

A food allergy is an allergic reaction to fragments of animal proteins in your cat’s food or treats. Typical food allergens are chicken meat and dairy. Other types of meat, like beef, fish or lamb, can also cause allergies.

3. Atopic dermatitis or atopy (environmental allergy)

Atopy is a condition that predisposes cats to allergies to substances in their environment, either inside or outside the house. Common examples of allergens vary from other species’ dander and dust mites to pollen and grass proteins.

4. Contact allergy

Contact allergy or hypersensitivity is a rare form of allergy to inorganic substances (e.g. household cleaners, deodorisers, rubber, textiles, plastics, metal). These trigger an allergy by binding to the proteins in the cat’s skin first.

Other cat allergies

Even rarer than other forms of allergies, mosquito bites can also trigger allergic reactions. The symptoms are the same as described above, but are localised to the nose or the ears - the places where cats are more likely to get stung. The allergens are the proteins in the bug’s injected saliva.

Though not being proteins, medications attach to proteins and can also cause an allergy. Drug allergies are thankfully extremely rare.

When to see your vet?

Because allergy symptoms only get worse with time and have great potential to cause your cat and yourself a lot of pain and distress, it is recommended that you speak to a vet as soon as possible if you think that your cat is allergic to something. The earlier a diagnosis is made and a management plan started, the better the chance of a successful control of the symptoms.

It’s not a good idea to medicate your cat with human medication for allergies, they are often ineffective in cats, make tests unreliable or can be outright dangerous for them.

How are allergies diagnosed and treated?

Allergic cats usually end up at the vet in the middle of a flare-up, with urgent problems - various degrees of itchiness, skin damage and infections, sore paws and ears, etc, so the short-term plan is usually aimed at treating those with antipruritics (anti-itching medication), antibiotics and anti-inflammatories and getting the cat comfortable asap.

After that, the medium/long-term plan is to figure out what kind(s) of allergy the cat has and what’s the best way to prevent or minimise future flare-ups.

When several allergies happen together, each contributes to the itchiness threshold. Sometimes, controlling the strongest allergy lowers the itchiness threshold enough to make addressing the others unnecessary.

Based on the cat's age and medical history, your account of the symptoms and a nose-to-tail exam of your cat to identify the most affected areas, vets make an educated guess as to which allergy is most likely and proceed to confirm or rule out that one first.

If both the history and examination of your cat don’t really point towards the most probable allergy, the only way forward is to confirm or rule out each common allergy one by one.

In such cases, the first step is to start on the outside, with parasites. Parasite allergy, especially FAD can be confirmed with a blood sample checking for antibodies against them. But most vets simply ensure that your cat has an effective flea prevention protocol. This works both as diagnosis and treatment, saving you time and money and your pet discomfort.

Should this not resolve all the symptoms, the next step is to consider food allergies. Antibody measuring tests are available for food allergies as well, but they are not very reliable, so vets prefer to trial a new food on your cat instead, again combining diagnosis with treatment.

If the food trial is not successful in reducing the symptoms either, atopy is the most probable option. Atopy is diagnosed based on your cat's history and exam and excluding other allergies. After that, your vet will recommend testing for specific indoor and outdoor allergens as this will help you avoid them where possible and get a tailored immunotherapy treatment.

A possible contact hypersensitivity or other rare allergy can be investigated if testing for environmental allergens does not support atopy, but as already mentioned, this is very rare. Most allergic cats that don't have flea-bite allergy or food allergy will be atopic.

Since hypersensitivity is a body peculiarity, in most cases it can’t be cured (yet), only successfully managed by avoiding the allergens and reducing the allergic reaction as much as possible.

Managing allergies requires a tight collaboration with your vet. They have the advantage of their medical knowledge, can perform tests and dispense medications and you can provide the essential first-hand information about your cat’s symptoms from your daily life with them. Both are equally important in the case of allergies.

So the best thing to start with is to put time and effort into understanding allergies as well as possible.

Even with the best efforts on your and your vet’s part, allergic flare-ups are not always avoidable. A successful management plan for an allergic cat is one that makes them as rare and as mild as possible, giving your pet a good, itch-free quality of life.

Allergies are one of those conditions where each pet's uniqueness really shines through, thus if you have allergy-related questions about your cat, please book an appointment with one of our vets who will be happy to help you with bespoke advice.