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Allergies in dogs: When the immune system goes crazy

Allergies are - on closer inspection - actually quite strange. Dogs, like humans, have a highly developed immune system that is able to distinguish between friend and foe and that defends us daily against all kinds of dangers - and then it allows itself to be provoked by such harmless substances as pollen or wheat protein!
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Why the immune system overreacts so much in allergic dogs and humans is still largely unclear. Perhaps the increase in allergies has to do with the fact that dogs, just like humans, now live in very hygienic environments, so their immune systems are – well – bored. But whatever the reason, allergies are now a big issue in dogs! It is thought that about one in 10 visits to the vet is due to an allergy.

And although allergies are usually not life-threatening, the suffering for both the affected dogs and their owners can be quite great. We have experienced this time and again as veterinarians in dermatology. It is therefore all the more important that dog owners know how to recognise an allergy at an early stage, what types of allergies there are and how they can be correctly diagnosed if the worst comes to the worst.

What types of allergies are there in dogs?

Dogs can actually be allergic to almost anything in their environment (e.g. plastic, detergents or medicines). In the vast majority of cases, however, it is one of three types of allergy: flea allergy, food allergy or environmental allergy.

Flea allergy

Flea allergy is actually the most common form of allergy in dogs. Here, the affected dogs react to certain substances in flea saliva. Whenever the dog is bitten by a flea, a small amount of flea saliva is also transferred. If the dog is allergic to this, the result is an exaggerated immune reaction and the dog becomes itchy. However, a flea allergy must never be confused with a flea infestation! In flea-allergic dogs, a single flea bite is enough to trigger severe symptoms – whereas even dozens of flea bites do not cause itching in dogs without a flea allergy. A flea allergy can therefore be responsible for allergic symptoms even if you have never found a flea on your dog.

Feed allergy

Dogs with food allergies react – as the name suggests – to certain ingredients in their food. Most common are allergies to beef, chicken and wheat. Theoretically, however, they can be allergic to anything they have ever eaten. Typically, dogs develop food allergies when they are quite young (about half of all affected dogs before their first birthday).

Environmental allergy

In the case of an environmental allergy (also known as atopic dermatitis), the immune system of the affected dogs reacts to substances in the environment that are actually completely harmless, such as pollen, grass, house dust, house dust mites or mould spores. It is therefore similar to hay fever in humans – except that dogs do not usually get a sniffly nose and watery eyes, but suffer from itching and skin inflammation. Dogs with environmental allergies usually show the first symptoms when they are between 6 months and 3 years old.

How do I know if my dog has an allergy?

The most typical – and usually the first – symptom of allergic dogs is itching. However, this does not necessarily have to be expressed by scratching; (increased) head shaking, nibbling, rubbing or licking also indicate that your dog is itching. Itching can vary in severity (from barely noticeable to bloody scratching), can occur all year round or only at certain times of the year, and can also affect different parts of the body.

Because the dogs work on the itchy areas with their teeth and claws and thus injure the skin, most dogs sooner or later develop 1) hairless areas and 2) inflammation. This can be recognised by reddening, crusts, scratch marks, pustules (small pus blisters) or even open/weeping wounds. If the inflammation or itching lasts longer, the skin can also thicken (development of so-called elephant skin) and darken. Bacteria and/or yeast fungi often take advantage of the damage to the skin and infect it. Such a so-called secondary infection aggravates the itching and inflammation even more.

In addition to these typical skin symptoms, ear infections and paw inflammations are also common, especially in dogs with food or environmental allergies. Watery eyes, sneezing and nasal discharge are also possible, but not as common (most likely in environmentally allergic dogs).

Especially in dogs with food allergies, digestive problems are often observed – these can range from intestinal rumbling, flatulence and more frequent defecation to diarrhoea and vomiting.

How can an allergy be diagnosed?

Unfortunately, this is often not so easy – and sometimes ensures that dog owners only receive the correct diagnosis after quite an odyssey!

Unfortunately, there is still no test to find out whether a dog suffers from an allergy, nor is there one that can say for sure what it is allergic to. The allergy tests that are very often carried out are only useful in very few cases – in most cases you could actually save the money for them (more on this below).

Instead, there is only one way to make the right diagnosis: you have to approach it slowly. The first step is to find out whether the dog is allergic at all. To do this, all other diseases that could be responsible for the symptoms must be ruled out (including a thorough preliminary discussion, a general examination, a detailed examination of the skin, examination for mites, etc.).

If it is then clear that it is an allergy, the vet will try to determine the type of allergy in the next step: Flea, food or environmental allergy. Unfortunately, there is no shortcut here either – the individual types of allergy have to be ruled out (or confirmed) one after the other through various “experimental treatments” (flea allergy: through effective flea prophylaxis; food allergy: through an exclusion diet of approx. 8 weeks). The different types of allergies can look so similar (especially food allergy and environmental allergy are often identical in symptoms) that this is the only way to distinguish them! In fact, environmental allergy is also a so-called exclusion diagnosis, i.e. it can only be diagnosed by excluding the other types of allergy.

In addition, the dog must be constantly monitored for the above-mentioned secondary infections with bacteria or yeast fungi – if any are present but not treated, all the experimental treatments can be meaningless. As a reminder, secondary infections can themselves lead to itching and inflammation. So even if the trial treatment is effective, the dog may still scratch. The consequence is then a misdiagnosis: for example, one thinks that the dog does not have a flea allergy, when in fact the infection is responsible for the persistent symptoms.

So you see – it can be very time-consuming and complicated to make the right diagnosis! It not only requires a lot of patience and cooperation from your side as the dog owner – a so-called allergy work-up is also quite time-consuming for the vet.

But it is worth the effort! It is better to go through a phase where you have to communicate a lot with the vet (and also go to regular appointments) than to treat the disease superficially for months or even years. This is something we have seen time and again in dermatology: at some point, most owners of allergic dogs will want to know exactly what the problem is (e.g. because side effects occur during treatment or the allergy gets worse). Although it is better late than never, most owners regret not taking this step sooner.

But now a brief word about allergy tests: Unfortunately, they are often carried out completely unnecessarily. In fact, there is only one situation where they make sense: when an environmentally allergic dog is to be treated by desensitisation (see below) and the vet wants to determine which allergens belong in his individual desensitisation solution. Allergy tests to find out which foods a dog can tolerate – or whether a dog is allergic at all – on the other hand, are a waste of money and time! This is because very, very often the results are wrong, i.e. they have no significance whatsoever. If you want to know more about this exciting topic: we have summarised the most important facts about allergy tests for you on fellomed (

Welche Behandlungsmöglichkeiten gibt es bei Allergien?

There is a whole range of different treatment options – starting with allergen avoidance (e.g. through regular flea prophylaxis in the case of flea allergy or change of feed in the case of feed allergy sufferers), through various remedies, medications and treatments that alleviate the symptoms, to causal treatment of the allergy by means of desensitisation.

Symptomatic treatment

There are many different options, which can be roughly divided into two categories: 1) strong medicines that reliably relieve itching and symptoms, but can also be associated with (stronger) side effects, and 2) “gentle” medicines that usually do not have many side effects, but often do not work as well.

Cortisone preparations, Apoquel®, Atopica® or Cytopoint® belong to the first category. All these medicines work very well (and usually very quickly) against itching, but unfortunately there can be various side effects – especially with prolonged administration (as an example: cortisone preparations e.g. ravenous appetite, weight gain, constant urge to urinate, immune deficiency, diabetes).

The second category, on the other hand, includes very well-tolerated treatments such as regular shampooing with special dog shampoo, essential fatty acids, skin care products and antihistamines. These remedies can also alleviate the symptoms – but they are often not sufficient as the sole therapy. However, they are excellent for supportive treatment! For example, they can often be used to reduce the dose of the “strong” medication, so that the risk of side effects is reduced.


Unfortunately, desensitisation is only an option for dogs with environmental allergies. The four-legged friend is treated with an allergen solution specially tailored to him, so that the immune system slowly gets used to the allergens and eventually no longer reacts to them. It is the only way to treat the allergy itself and is therefore also considered the best treatment option for dogs with environmental allergies.

Treatment of secondary infections

Of course, treatment also includes fighting existing infections. However, it does not always have to be an antibiotic – in most cases, antibacterial shampoos, foams or wipes are sufficient.  Who do I contact if I suspect an allergy in my dog?

In principle, you can of course go to any vet if you fear that your dog is suffering from an allergy. However, in veterinary medicine – just like in human medicine – there are specialists for the different fields and so of course also for skin diseases!

So if your dog is affected by an allergy (or you suspect it): especially with this disease, which is so complex and complicated both in diagnosis and treatment, it is definitely worth seeing a specialist veterinarian or even a Diplomate (international specialist veterinarian; highest level of qualification) for dermatology. After all, we go to the dermatologist with a skin disease – and not to the family doctor.  Although specialists are a bit more expensive at first (and maybe the journey is longer) – in the long run it is usually a worthwhile and sensible investment!

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The information contained in this veterinary article is for general information purposes only. It does not constitute individualised treatment recommendations for a specific animal. It is strongly recommended that you always discuss and clarify any symptoms or illnesses of your pet with a qualified veterinarian.