Does your cat show signs of itching, overgrooming, hair loss or even skin sores? If you’ve heard of it in dogs, you may be wondering if atopy could be to blame. But what is atopy – and can cats get it?
Table of contents
- What is atopy?
- How common is atopy in cats?
- What are the symptoms of atopy in cats?
- How can atopy be differentiated from Flea and Food Allergies?
- So how is atopy diagnosed?
What is atopy?
Atopy, also known as atopic dermatitis, is a common cause of itchy, inflamed skin in dogs. But it can also be seen in cats. It can be defined as an allergic skin condition caused by hypersensitivity to allergens in the environment, mediated by a specific type of antibody: IgE.
However, alongside atopy we can also see allergic skin disease in cats caused by other types of allergy. The current categorisation of allergic skin disease in cats separates it into 3 main conditions:
- Flea Allergy Dermatitis – a hypersensitivity dermatitis triggered by flea bites.
- Feline Atopic Skin Syndrome – allergic skin disease triggered by environmental allergens like pollen, dust mites and mould. Often colloquially termed ‘atopy’, this condition has previously been described as non-flea non-food hypersensitivity dermatitis.
- Food Allergies – skin changes associated with a dietary allergy, seen with or without gastrointestinal symptoms.
Technically, atopy describes a genetic predisposition to atopic dermatitis which has yet to be proved in cats. However, environmentally induced allergic dermatitis in cats is frequently referred to as atopy, so that’s the term we’ll use here.
How common is atopy in cats?
While allergic skin disease is relatively common in cats, Flea Allergy Dermatitis is by far the most common type. In contrast, although atopy is reportedly the second most common type of feline allergic skin disease, it’s relatively rare.
What are the symptoms of atopy in cats?
Cats with atopy typically start to show signs before 3 years of age. But the symptoms often worsen over time and mild symptoms may be missed. Initially, many cats have seasonal symptoms but this can progress to year-round skin disease; it also depends on the allergens involved as specific pollens may only be seen in spring, whilst other common allergens like dust mites are present year round.
Symptoms are broadly divided into 4 groups, and affected cats may show just one or several of these.
Most commonly seen in Flea Allergy Dermatitis, miliary dermatitis may also be caused by atopy in some cats. Affected cats usually have diffusely distributed, small raised red bumps on the skin over their back, especially near the base of their tail; these are usually crusty or covered by scabs.
Many skin conditions can cause fur loss (alopecia), including atopy. In allergic skin disease, this is usually symmetrical, often over the back and flanks, and self-induced as a result of overgrooming in response to itching (pruritus).
Head and neck self-trauma
Intense itchiness due to allergic skin disease can cause cats to scratch and injure themselves around the head and neck. This often results in open sores, scabs and fur loss in these areas, especially around the mouth, eyes and ears.
Eosinophilic Granuloma Complex (EGC)
This is a group of inflammatory skin conditions. The causes of EGC are not fully understood but can include allergic skin disease. EGC may appear as eosinophilic ulcers on the lips, eosinophilic plaques (usually on the belly) or nodular, raised eosinophilic granulomas. These conditions can also cause intense itching and may require additional treatment, frequently in the form of immunosuppressive medication.
Read more about eosinophilic granuloma complex.
How can atopy be differentiated from Flea and Food Allergies?
Skin problems caused by allergies can appear very similar – a cat with atopy may show any of the symptoms above but it’s not possible to fully rule out Flea Allergy Dermatitis or food allergies based on symptoms alone.
However, some symptoms are more common in different conditions. Food allergies and atopy are more likely to cause symptoms on the head and neck, whereas Flea Allergy Dermatitis is much more commonly associated with miliary dermatitis over the back (although often it does spread to the head too). In addition, age can also help us with diagnosis – cats with atopy typically start to show symptoms under 3 years of age, whereas food allergies can develop much later.
So how is atopy diagnosed?
Unfortunately, there isn’t a simple test for atopy. Diagnosis is based on history, clinical signs and excluding other possible causes – including other types of allergy and conditions like mites and fungal infections.
If your cat’s symptoms are consistent with conditions like mites or a fungal infection, your vet may recommend a skin scrape or other tests.
In contrast, ruling out Flea Allergy Dermatitis sounds simple – if you look at your cat and see no fleas, you might reasonably assume they’re not a problem. However, many itchy cats with a low flea burden groom so fastidiously that no obvious fleas, or even flea dirt, may be visible.
First things first
As a vet, if I see a cat with allergic skin disease I recommend a thorough course of flea treatment for all cats and dogs in the household (which may harbour fleas without showing any symptoms!), as well as thorough cleaning of the home. Eliminating a flea infestation can take up to 3 months of regular flea treatment, but your cat’s symptoms should begin to improve much sooner if fleas are responsible.
Then rule out food allergies
If there’s still no improvement with flea treatment, a diet trial may be recommended. This usually involves at least 6-8 weeks of feeding only a hypoallergenic diet (for example, those by Purina, Hill’s or Royal Canin). Unfortunately, any treats, titbits or even food from neighbours can undo all this hard work, so it’s essential to make sure this is the only food they get.
If fleas and food are ruled out…
If there’s still no (or limited) response, but your cat’s history, symptoms and response to medication is consistent with allergic skin disease, it’s likely that your cat has atopy.
It’s important to note that cats can suffer from multiple types of allergic skin disease at the same time – so if there’s a partial response to some of these measures, your cat could have atopy alongside a food or flea allergy.
In terms of medication, steroids (like prednisolone) are the typical first line treatment to reduce allergy-associated inflammation, but once a diagnosis has been made your vet may suggest trialling other medications with fewer long-term side effects.
What about blood tests?
You may have heard of blood tests for allergies in cats and dogs – so why can’t we use them to get a diagnosis? Unfortunately, no blood test can diagnose these conditions in cats. There is a blood test we can use to identify what allergens a cat (or dog) is allergic to for immunotherapy treatment, once a diagnosis has been made – but it sadly isn’t useful for diagnosis.
You may also come across sites offering hair or saliva tests for allergies – unfortunately, there is no evidence for these being clinically useful.
While treatment of feline atopy is outside the scope of this article, it’s important to note that there are several treatment options available which can hugely improve your cat’s quality of life. It’s important to discuss your cat’s specific situation with your vet and form a plan for diagnosis and treatment. While we can’t cure atopy, most affected cats live long and happy lives with the right care.
Further Reading and references:
- Bajwa J. (2018). Atopic dermatitis in cats. The Canadian veterinary journal = La revue veterinaire canadienne, 59(3), 311–313. Access here
- Halliwell, R., Pucheu-Haston, C.M., Olivry, T., Prost, C., Jackson, H., Banovic, F., Nuttall, T., Santoro, D., Bizikova, P. and Mueller, R.S. (2021), Feline allergic diseases: introduction and proposed nomenclature. Vet Dermatol, 32: 8-e2. Access here
- Jackson, H., & Marsella, R. (Eds.). (2012). BSAVA Manual of Canine and Feline Dermatology (3rd ed.). British Small Animal Veterinary Association.
- Harvey, A., & Tasker, S. (2013). BSAVA Manual of Feline Practice: A Foundation manual. British Small Animal Veterinary Association. Available here