Pet Allergies

Millions of us have pets as part of our families but frustratingly in people with an allergic tendency, it is not uncommon to develop allergy to furry animlas particularly cats, dogs and less commonly horses, rabbits and other small mammals, such as hamsters or guinea pigs. This can create real problems for family members if there is a pet, particularly living inside the home, but can also be an issue when visiting family and friends who keep pets, making even short visits problematic and in the worst-case scenario, resulting in significant symptoms such as exacerbations of asthma. 

What is a pet allergy?

Pet allergies occur when the immune system misinterprets the harmless nature of proteins from animals and as a result reacts to them. These allergenic proteins known as ‘dander’ come from the hair, skin and particularly the saliva of animals such as cats and dogs and can provoke significant reactions particularly from the respiratory system leading typically to nasal and eye symptoms.

What causes pet allergies?

Due to the very light weight of cat allergen (which has the technical name of Fel d 1) and is found predominantly in cat saliva, this tends to be the most potent allergen and the most common cause of pet allergies. However, dog allergen (Can f 1) is also a significant issue particularly in dogs that shed a lot of dander. Allergy to horses is also common amongst those who have lots of contact with them.

What are pet allergy symptoms?

For most people, allergies will cause nasal symptoms such as itchiness, sneezing, a runny nose and nasal congestion. Symptoms can also affect the eyes with itchy, runny eyes. In more severe cases, the eyes can swell up and there can also be features of asthma such as wheezing and airway tightness. In some people, exposure to the animals that they are allergic to, can contribute to making their eczema worse. 

How to know if you have pet allergies?

If you do not have a pet yourself but find that you develop the symptoms detailed above every time you go into the home of somebody who has a pet or go near a pet, particularly if a cat or dog licks you (which can often cause hives), then the diagnosis is relatively clear. However, if you have an animal living in your own home, it can be less obvious as the symptoms can be more chronic. Typically, they will involve nasal symptoms particularly nasal congestion. You might notice that when you spend time away from home, for example on holiday when your pets are not with you, that your symptoms improve. If you do suspect a pet allergy, then it is helpful to get an allergy test to confirm this.

What to expect from your pet allergy test?

There are two types of tests that are useful at confirming a pet allergy. The first is a skin prick test where a small amount of the relevant allergen is put onto the forearm and a gentle scratch made with a lancet. In the next few minutes, a little red bump will develop due to histamine release. The larger this is, the more likely it is that you have an allergy to that pet. An alternative test is a blood test which looks for the level of allergic antibody (IgE) to a specific animal in the bloodstream. Again, the higher the level, the more likely it is that there is an allergy. It is important to remember that these tests do have to be interpreted carefully in the context of symptoms that develop. If you do not get symptoms when you go near the pet even if the level on the test is high, it is unlikely to represent a genuine allergy. The tests essentially help confirm what the clinical history already strongly suggests.

How long do pet allergy symptoms last?

Pet allergy symptoms typically develop after a period of exposure to the animal – this may not necessarily be in your own home but could be through contact with others who are pet owners or visiting their homes. Typically, they do not develop in early childhood as a fairly long period of years of exposure is required, so typically symptoms do not show themselves until later childhood. Once an allergy is established, it tends to last some time. Often patients will report their symptoms improving over time when they have the pet at home which may well happen but can sometimes be a misinterpretation of simply getting used to the symptoms as they become more chronic and not noticing them as being out of the ordinary anymore.

How are pet allergies treated?

There are three main methods to treat a pet allergy. 

Avoidance:  This effectively means rehoming the pet or avoiding visiting places where the animal may be present. Just avoiding the animal themselves may not be enough as for example, with cat allergen, even if the cat is not present in somebody’s home, there will still be a lot of dander around which can taken months or even years to clear after the animal has been removed. Of course, as pets are very much part of the family, rehousing may not be an option especially if symptoms are only relatively mild, although it is always a good idea to ensure that the pets are kept out of the allergy sufferer’s bedroom completely as this is where long periods of exposure could otherwise happen if the pet has spent time on the patient’s bed. 

Medication:  Simple things such as saline nasal sprays can be very helpful here but if this is not quite enough then consideration should be given to long-acting non-sedating antihistamines (which can be purchased over the counter), or steroid nasal sprays can also be helpful. In some cases, eye drops or increased levels of asthma or eczema treatment may be required, but at this point allergen avoidance needs to be given more careful consideration. 

Pet desensitisation: This is a treatment that involves small but increasing deliberate exposure to large amounts of pet allergen that are sprayed or dropped under the patient’s tongue. Over time, this retrains the immune system to be less reactive to the causative allergen. It is not really designed to allow patients with significant symptoms to have the animal in their home but can be very helpful for patients who have intermittent exposure, for example, when they visit grandparents’ or friends’ homes and get troublesome symptoms as a result of contact with a particular animal. The process of desensitisation is safe and is done on a regular daily basis at home. Sometimes a combination of all three strategies is required to get on top of things. 

More recently, there have also been some innovative strategies developed to help reduce the symptoms of pet allergies. These include the development of cat food (Purina Pro Plus Liveclear) which contains a substance which binds to the main cat allergen reducing the amount that is given off by the cat, hence reducing its allergenicity. This is unlikely to be enough to prevent severe symptoms in somebody with a significant cat allergy but can be part of a solution if used with the other options above.

Do pet allergies go away with exposure?

Low levels of pet exposure in allergic individuals tend to cause ongoing symptoms whereas significantly larger exposures can cause desensitisation, although this is difficult to achieve without formal treatment with allergen extract. Some people feel that ongoing exposure does improve their symptoms, but this can often be a misinterpreting of them simply getting used to more chronic symptoms. A typical situation will be children who feel that their allergies are well-controlled but then when they go away, for example, to university and come back months later, they have significant reactions to the pets that they have been away from. 

How long do pet allergies last after exposure?

Allergic symptoms will continue as long as the exposure continues. Once the allergen is removed, symptoms usually settle within a few hours but can last for 2-3 days, for example if there has been significant eye swelling, the use of antihistamines and on some occasions even oral steroids can help this settle more rapidly.

Can you outgrow pet allergies?

It is possible to outgrow pet allergies but like other respiratory allergies, once they develop in later childhood, they do tend to run a protracted course.

Can pet allergies be prevented?

It is common to be asked whether it is safe for a child with other allergies such as food allergies to get a cat or a dog, and if testing at the time to the animal is negative, it is unlikely that the child is already allergic. However, it is important to bear in mind that patients with an allergic tendency will typically develop allergies after a period of regular exposure, so if such a patient brings a cat or a dog into their home, there is a very high chance that they will eventually become allergic to it and that will then start to cause symptoms which could be problematic. It is therefore worth discussing this before going down the route of purchasing a pet.

Written by

Professor Adam Fox

Date reviewed: November 2021

Adam Fox is a Professor of Paediatric Allergy with over 20 years experience in both the NHS and private sector. Professor Fox is Commercial Medical Director at Guy’s & St Thomas’ Hospitals NHS Foundation Trust and Professor of Paediatric Allergy at King’s College London and the founding Director of the KCL Allergy Academy, a postgraduate educational programme, which was a finalist at the BMJ Awards in 2018.

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Pet Allergies

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