Cat Allergy
Cat allergy is one of the most common and clinically significant forms of pet-related allergy, with an estimated prevalence of between 10 and 20 per cent in the allergic population. Unlike pollen allergies, it is a year-round condition: exposure to the allergen can occur throughout the year, regardless of the season. What sets it apart from all other animal allergies is the extraordinary ability of the main allergen – Fel d 1 – to spread and persist in indoor environments: it can be detected in homes, schools, offices and on public transport even in the absence of a cat. This ubiquity makes avoidance particularly difficult and requires an active management plan, to be drawn up with a specialist doctor.
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What is cat allergy and why is it perennial?
Cat allergy is an IgE-mediated respiratory allergic condition caused by the inhalation of allergens produced by cats. Unlike hay fever – which is characterised by a clearly defined season – cat allergy is a perennial form of allergy: symptoms can appear and persist at any time of year, with varying intensity depending on the degree of exposure, and may sometimes worsen during the annual periods when the cat’s coat is shedding.
The main source of allergens is not the animal’s fur itself, but its saliva, secretions from the sebaceous glands in the skin, and urine. Whilst grooming, the cat continuously spreads saliva over its coat; from there, the allergens settle on the hairs and are dispersed into the environment in the form of microscopic particles that are easily inhaled.
The prevalence of cat allergy is on the rise in many countries, in parallel with the increase in the proportion of households with pets. In Italy, the cat is the most common pet, with over 9 million cats, making this allergen one of the most ubiquitous in indoor environments (i.e. confined to indoors).
Dabrowski AJ, Van der Brempt X, Soler M, et al. Cat skin as an important source of Fel d I allergen. J Allergy Clin Immunol 1990; 86: 462–465.
Charpin C, Mata P, Charpin d, et al. Fel d I allergen distribution in cat fur and skin. J Allergy Clin Immunol 1991; 88: 77–82.
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Fel d 1: the allergen that goes beyond the cat
The main cat allergen is Fel d 1, a glycoprotein produced predominantly by the skin’s sebaceous glands and saliva. Fel d 1 is recognised by the vast majority of patients sensitised to cats (over 90 per cent of cases) and is the reference molecular marker for primary sensitisation.
The physicochemical characteristics of Fel d 1 make it exceptionally diffusive and persistent compared with allergens from other animals:
- Very small size (less than 5 µm): particles carrying Fel d 1 remain suspended in the air for hours after being released into the environment and easily reach the lower airways
- High electrostatic charge: it adheres strongly to surfaces, fabrics, clothing, carpets and hair
- Extraordinary environmental persistence: it can remain detectable in environments for months after the cat has been removed – in some studies for up to 6 months or more – unless specific cleaning measures are taken
- Passive transport: it is easily transferred onto clothing and can be found in schools, offices, public transport and homes where the cat has never been
This combination of characteristics makes Fel d 1 one of the most difficult indoor allergens to avoid among all those currently known. Even people who do not live with a cat may be exposed daily to clinically significant levels of Fel d 1.
Other cat allergens (such as lipocalins and albumins) can trigger allergic reactions and cross-reactivity with the fur of other animals and with the meat of certain mammals.
[Ref
Dávila I, domínguez-ortega J, Navarro-Pulido A, et al. Consensus document on dog and cat allergy. Allergy 2018; 73: 1206–1222.
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Custovic A, Simpson A, Pahdi H, et al. Distribution, aero - dynamic characteristics, and removal of the major cat allergen Fel d 1 in British homes. Thorax 1998; 53: 33–38.
Symptoms of cat allergy
Symptoms typically appear within a few minutes of exposure to cat allergens and may be present on a continuous basis in people who live with a cat or who spend time in environments with high concentrations of the allergen. Unlike hay fever, symptoms may persist throughout the year, with varying intensity.
The severity and rapid onset of symptoms – often within 15–30 minutes of entering an environment with a high concentration of Fel d 1 – are among the most characteristic clinical features of cat allergy and often distinguish this condition from other forms of rhinoconjunctivitis and asthma.
Nwaru BI, Suzuki S, Ekerljung L, et al. Furry animal allergen component sensitization and clinical outcomes in adult asthma and rhinitis. J Allergy Clin Immunol Pract 2019; 7: 1230–1238.e4.
Nasal symptoms
- Repeated sneezing, sometimes in prolonged bouts
- Nasal itching
- Profuse watery nasal discharge
- Nasal obstruction, including persistent obstruction
Eye symptoms
- Intense itching and redness of the eyes
- Excessive watering of the eyes
- Swelling of the eyelids in severe cases
Bronchial symptoms
- Dry cough
- Wheezing
- Dyspnoea (shortness of breath)
- Feeling of chest tightness
Skin reactions
- Urticaria or erythema at sites of direct contact with cat hair
- Exacerbation of atopic eczema in susceptible individuals
Cat allergy and asthma
Of all pet allergies, cat allergy is the one with the greatest documented impact on bronchial asthma. Continuous, year-round exposure to Fel d can promote chronic airway inflammation, bronchial hyperreactivity and progression to more severe forms of asthma. However, appropriate management can limit these effects.
The small size of the allergenic particles allows Fel d 1 to penetrate deep into the lower airways, right down to the bronchioles, triggering an inflammatory response in the lungs even at low levels of exposure. In people with asthma, this mechanism can lead to exacerbations even in environments where no cat is present but where the allergen has been passively transported.
The international scientific consensus documents GINA and ARIA, on the management of allergic rhinitis and asthma, emphasise that controlling exposure to indoor allergens – including those from pets – is an integral part of optimal asthma management. For asthmatic patients with a confirmed cat allergy, the treatment plan must always include an assessment of environmental exposure and applicable reduction measures.
Custovic A and Chapman Md. Indoor allergens as a risk factor for asthma. In: Barnes PJ, Grunstein MM, Leff A,
et al (eds). Asthma. Philadelphia: Lippincott-Raven, 1997, pp 83–103.
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Platts-Mills TA, Ward GW, Sporik R, et al. Epidemiology of the relationship between exposure to indoor allergens and asthma. Int Arch Allergy Appl Immunol 1991; 94: 339–345.
Global Initiative for Asthma. Global Strategy for Asthma Management and Prevention, 2025. Updated 15 November 2025. Available from: www.ginasthma.org.
Variability in Fel d 1 production
Not all cats produce the same amount of Fel d 1. The literature reports that certain biological factors influence the production of the allergen:
- Sex: unneutered males produce, on average, greater quantities of Fel d 1 than females and neutered males
- Neutering: neutered cats produce less allergen than unneutered cats, although the reduction is not sufficient to eliminate the allergy risk
- Breed: some breeds (e.g. Siberian, Norwegian Forest Cat, Bali) are reported in the literature to be associated with lower Fel d 1 production, although there is considerable individual variability within the same breed
- Age and health status: production may vary depending on the animal’s age and general condition
It is important to emphasise that there are no completely hypoallergenic cats. Even breeds associated with lower Fel d 1 production can trigger significant allergic reactions in sensitised individuals. Each patient’s individual response depends on many factors – reactivity threshold, level of exposure, presence of other sensitivities – and cannot be predicted on the basis of the animal’s breed or sex. The assessment of individual tolerance must be carried out by a specialist.
Grönlund H, Saarne T, Gafvelin G, et al. The major cat allergen, Fel d 1, in diagnosis and therapy. Int Arch Allergy Immunol 2010; 151: 265–274.
Zielonka TM, Charpin d, Berbis P, et al. Effects of castration and testosterone on Fel dI production by sebaceous glands of male cats: I – immunological assessment. Clin Exp Allergy 1994; 24: 1169–1173.
Reducing exposure: practical measures
The most effective measure for reducing exposure to Fel d 1 is to remove the cat from the home. However, even after the animal has been removed, allergen levels in the environment may remain high for months, requiring specific cleaning measures. In cases where removal is not possible or is not accepted by the patient, the specialist will assess the exposure-reduction measures applicable as part of an overall treatment plan.
Measures in the home
- Do not allow the cat access to the bedroom or to rooms where the patient spends most of their time
- Replace carpets, rugs and textiles that trap allergens with hard surfaces (parquet, flooring, furniture made of non-porous materials) that are easy to clean
- Vacuum more frequently using a vacuum cleaner fitted with HEPA filters specifically designed for allergens
- Install air purifiers with HEPA filters in rooms where the patient usually spends time
- Wash surfaces that the cat comes into contact with frequently
- Washing the cat regularly (roughly once a week) can temporarily reduce the amount of allergen on its coat, although the effect is short-lived
Exposure-reduction measures are complementary to drug therapy and any allergen-specific immunotherapy, as part of an individualised treatment plan agreed with a specialist doctor. Their effectiveness varies and depends on the patient’s specific living situation and clinical profile.
Ref
Wood R.A. et al. The effect of cat removal on allergen content in homes. J Allergy Clin Immunol, 1989.
Nicholas C, Wegienka G, Havstad S, et al. Influence of cat characteristics on Fel d 1 levels in the home. Ann Allergy Asthma Immunol 2008; 101: 47–50.
Avner dB, Perzanowski MS, Platts-Mills TAE, et al. Evaluation of different techniques for washing cats:
quantitation of allergen removed from the cat and the effect on airborne Fel d 1. J Allergy Clin Immunol 1997; 100: 307–312.
Liccardi G, d’Amato G, Russo M, et al. Focus on cat allergen (Fel d 1): immunological and aerodynamic characteristics, modality of airway sensitization and avoidance strategies. Int Arch Allergy Immunol 2003; 132: 1–12.
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furry animals. Ann Allergy Asthma Immunol 2012; 108:223.
Björnsdottir US, Jakobinudottir S, Runarsdottir V, et al. The effect of reducing levels of cat allergen (Fel d 1) on clinical symptoms in patients with cat allergy. Ann Allergy Asthma Immunol 2003; 91: 189–194.
Frequently asked questions
Lockey RF. The myth of hypoallergenic dogs (and cats) [Editorial]. J Allergy Clin Immunol 2012; 130: 910–911.
Gulbahar o, Sin A, Mete N, et al. Sensitization to cat allergens in non-cat owner patients with respiratory allergy. Ann Allergy Asthma Immunol 2003; 90: 635–639
Dhami S and Agarwal A. Does evidence support the use of cat allergen immunotherapy? Curr Opin Allergy Clin Immunol 2018; 18: 350–355.
Demoly P, Zakariya M, Dávila I, Scibilia G, Ortolani V, Domínguez-Ortega J, Bergmann KC, Gevaert P, Didier A. Allergy to Cats: Current Perspectives and Therapeutic Options. Clin Transl Allergy. 2026 Mar;16(3):e70152.
Yes. Fel d 1 is easily transferred onto the clothing of people living with a cat and can be released into the environment in public places such as schools, offices, public transport and the homes of friends or family members. Environmental studies have detected traces of Fel d 1 in almost all the schools and workplaces investigated, even in the absence of cats. Sensitisation can also develop through this indirect exposure, although the intensity of exposure tends to be lower than when living directly with the animal.
No, not immediately. Even after the cat has been removed, Fel d 1 can remain in the environment for several months, particularly on carpets, textiles, sofas and in areas not easily reached by routine cleaning. The improvement in symptoms is gradual and depends on the thoroughness of the environmental cleaning measures taken. Patients should be prepared for this delayed effect to avoid misinterpreting the clinical course.
No. All cats produce Fel d 1, although the amount varies depending on sex, breed and whether the cat is neutered. So-called ‘hypoallergenic’ breeds produce, on average, less allergen, but there is considerable individual variability within the same breed, and it is not possible to predict a patient’s allergic response based on the animal’s breed. The term ‘hypoallergenic’ is not scientifically validated in an absolute sense: any cat can trigger reactions in a sensitised individual.
Not necessarily, but the answer depends on the severity of the allergy and whether the person has bronchial asthma. In people with mild to moderate allergy that is controlled by treatment, living with a cat can be managed with appropriate environmental measures and a suitable treatment plan. In people with asthma that is difficult to control or who experience severe reactions, a specialist will assess whether removing the cat is necessary for the e l control of the condition. In any case, this decision must be made in consultation with an allergist, based on the individual’s clinical profile.
Yes. Allergen-specific immunotherapy (AIT) using cat extracts is available and can help reduce symptoms and bronchial hyperreactivity. Suitability for AIT must be assessed by an allergist, taking into account the clinical profile, the severity of symptoms and any co-sensitisation.
Yes, it is possible. Fel d 1 sticks to the clothes and hair of people living with a cat and can be transferred through indirect contact. In highly sensitised individuals, even this type of exposure can be enough to trigger symptoms, particularly in the eyes and nose. This highlights the difficulty of completely avoiding the allergen and the need for an active treatment plan.
You should see a doctor if you experience nasal, eye or bronchial symptoms that appear or worsen when you are in the presence of cats or enter environments where cats live, or if these symptoms are inexplicably present on a continuous basis throughout the year. An allergy assessment involving skin prick tests and, where indicated, molecular diagnostics, enables the diagnosis to be confirmed, the sensitisation profile to be determined and the most appropriate treatment plan to be established.
Practical insights
Information notice
The information contained on this page is for informational purposes only and is not a substitute for the advice of a doctor or other qualified healthcare professionals. For a clinical assessment and any therapeutic decisions, including diagnosis, environmental management and the choice of treatments, you should consult your specialist allergist. The practical guidelines provided are intended as informative support measures within the context of an individualised treatment plan.
Bibliography
- Bousquet J. et al. Allergic Rhinitis and its Impact on Asthma (ARIA) 2019 Update. Allergy, 2020.
- Roberts G. et al. EAACI Guidelines on Allergen Immunotherapy. Allergy, 2018.
- Custovic A., Simpson A. The role of inhalant allergens in allergic airways disease. J Investig Allergol Clin Immunol, 2012.
- Canonica G.W. et al. Allergic asthma: indoor allergens and disease control. Allergy, 2013.