Itching in dogs

All dog owners are familiar with their dog scratching once in a while. Increased scratching can often occur during the moulting phase in particular. However, if you observe that this itching goes beyond a normal level and your dog is also licking and cleaning itself more often, you should urgently follow up on it. Itching can hugely limit a dog’s wellbeing and reduce its quality of life. Sometimes itching is so bad that neither the dog nor the owner can sleep any more.

Itching can manifest in very different ways. The owner usually notices the dog scratching different parts of its body with its front or rear paws. This can affect all parts of the dog’s body. For instance, shaking its head means that the ears are itching. Dogs lick and also fiddle with the paws or legs, or even the back and croup. If dogs have limited or no access at all to certain areas of their body, they rub them against the wall or carpet to reduce their itching. In many cases, however, it doesn’t just stop at itching. Cats can suffer from inflammations through constant scratching and bacteria, yeast fungi and other pathogens can pave the way for infections. Skin infections increase itching on top of everything, so the dog becomes trapped in a vicious circle of itching.

Causes of itching for dogs

Itching is one of the most common reasons for taking a dog to the vet. Many different causes and illnesses can trigger itching. We would like to show you the most important ones here:

We differentiate between primary and secondary causes: amongst the primary causes of itching, itching is present first and only then do skin changes occur. In contrast, we first see changes to the skin and then itching with secondary causes.

Ectoparasites

Cheyletiella (predatory mites)

This type of mite is often overlooked although it is common. Cheyletiella aren’t specific to a certain host and are found with dogs, cats and rabbits, whilst humans are accidental hosts. They are transmitted by direct contact or through the environment. Predatory mites live very superficially on the skin and feed off tissue fluid. Itching caused by predatory mites can greatly vary in intensity, though is mostly limited to the back, shoulders and possibly the outside of the dog’s ears. The formation of dandruff, particularly on the back, is a typical feature.

Sarcoptes (scab mites)

Scab mites are very specific to a certain host, highly contagious and zoonotic (transmissible to humans). They are transmitted by direct contact with affected dogs or through the environment. Scab mites dig tunnels into the keratin layer of the dog’s skin and lay eggs and faeces there. They feed off dead skin cells and tissue fluid. Itching occurs on the one hand due to the mites themselves, as well as due to an allergic reaction to their metabolites. The itching is usually almost insatiable and remains even at night and if you try to distract your dog. It mainly affects the earlobes, joints (elbows, knees and ankles) and the stomach and chest, then later the entire body.

Harvest mites (Trombicula autumnalis)

Harvest mites are pinhead-sized orange-red parasites mainly found in summer and autumn. Their larva feeds off their host’s lymphatic fluid. They are transmitted in tall grass, where they wait for their host and mainly attack the paws (between the toes), stomach (especially the teats) and head. With sensitive animals in particular, the bite of the larva can cause allergic reactions with severe itching. Itching may persist for a while even after the parasites have been removed.

Ear mites (Otodectes cynotis)

Since ear mites are very specialised, they preferentially attack the outer ear canal and rarely the skin surrounding the ear too. All development phases of ear mites feed off the dog’s surface tissue fluids and dead skin cells. They are transmitted by direct contact with infected animals and puppies are mostly affected, rarely adult dogs. Severe itching inside the ears and the area surrounding them is typical of an ear mite infestation.

Fleas

A flea infestation is a common cause of itching in dogs. Fleas are transmitted to dogs by infected animals or through the environment during their young development phases (e.g. sleeping spots or cars). Itching caused by flea infestations primarily affects the back and base of the tail, as well as the stomach, inner thigh and throat. Flea allergy dermatitis (FAD) or flea saliva allergy can also be caused by hypersensitivity to flea saliva allergens.

You can find more information on fleas in the article “Fleas on dogs”.

Allergies (contact allergies, flea saliva allergies, food allergies, environmental allergies (atopy))

Different allergies can cause mild to severe itching in dogs.

With contact allergies, just about any allergen (plants, synthetic substances) can trigger an allergic reaction in sensitive dogs at the point of contact, often a hairless area of the skin. Itching is mostly limited to the contact area with the allergen.

Flea saliva allergy or flea allergy dermatitis (FAD) is the most common allergy affecting dogs. It can be caused by all flea species, though mostly by the less host-specific cat flea (Ctenocephalides felis). The allergens in flea saliva enter the dog’s body when the flea bites. Even a small number of fleas, sometimes even just one, can trigger an allergic reaction. Affected dogs mainly suffer from itching on their rear body: on the lower back, base of the tail, tail, rear legs and on the stomach too. Since dogs scratch or bite themselves so badly when suffering from severe itching, self-inflicted skin changes can come about in addition to flea bites, e.g. what are known as hot spots. Since these areas of the skin are often infected by bacteria or yeast fungi, these infections cause additional itching (known as a secondary infection).

Atopy is an allergy to environmental allergens such as pollen, grass, house dust mites or mould. Itching is usually on a seasonal basis, for instance, during the pollen season. Allergens enter the dog’s body through the skin. The preferred itching areas with atopy are the face and paws, legs, stomach and inner thigh, whilst the ears too are commonly affected. As with FAD, further changes to the skin with secondary infections can increase itching due to constant scratching. With food allergies, an allergic reaction to a component (protein) in food occurs. It is the third most common allergy affecting dogs after FAD and atopy. The triggering factor is mostly a food that dogs have already consumed for a long time. Allergens enter the dog’s body through the intestine. Food allergens are large protein molecules. In our part of the world, primarily beef, milk and dairy products, eggs, chicken, wheat, fish and soy are significant allergens. Often falsely demonised, grain is not an allergic trigger per se, whilst wheat protein or another grain protein can trigger allergies in rare cases. However, what are known as triggers are not more allergenic than other substances; dogs simply come into contact with them most frequently. The distribution pattern for itching is very similar to that of atopy and is therefore not typical of food allergies. Itching mostly occurs four to 24 hours after contact with the allergen and most commonly affects the face, ears, paws, shoulders and inner thigh.

Fungal infection (dermatophytes)

In addition, Microsporum canis or on rarer occasions Trichophyton mentagrophytes infections can lead to itching in dogs. Fungal infections are quite rare, essentially only with immunosuppression, inadequate care or close contact with an infected animal. Transmission occurs through highly resistant fungal spores from the environment or infected hairs. Itching comes to the fore on areas that enter into contact with infected hairs or in the case of T. Mentagrophytes, areas with direct contact with the floor like the face and legs or paws.

Secondary causes of itching are mainly systemic diseases, which weaken the immune system.

Diverse changes to the skin and fur can result from some diseases like hypothyroidism, Cushing’s disease (hyperadrenocorticism) or even autoimmune diseases. They develop due to deficiencies in the skin’s protective barrier, a weakened immune system, a slowing of the hair cycle or with Cushing’s, thin and inelastic skin due to excessive cortisone production. These diseases first emerge in the form changes to the skin without itching. Due to changes to the structure of the skin and suppression of the immune system, infectious agents like bacteria and yeast fungi (Malassezia) have an easy time of it. They position themselves on the altered skin and trigger an infection. These are called secondary infections, because they are based on an existing ailment and in turn cause itching. In these cases, itching depends on the intensity of the secondary infection.

Demodicosis

With demodicosis, mites feed off tissue fluid and cell waste just like other mites, but they store their faeces in their own cells, so it doesn’t trigger an allergic reaction in dogs. Changes in the skin due to demodex mites mostly don’t involve itching. It almost only occurs in a generalised form and only after colonisation of the skin change due to bacteria and yeast fungi, making it secondary.

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Diagnostic approach for itching

Since there are so many reasons why dogs can suffer from itching, an extensive anamnesis and precise preliminary report are the basis for a structured approach to diagnosis by the vet. We can already get helpful pointers from descriptions and preliminary reports. The following points are particularly important:

• Descriptions, i.e. breed, sex, age, size and weight
• Age when the itching problem began
• Similar symptoms with the parents and/or siblings from the same litter
• Location of itching
• Seasonality
• Whether other animals or humans in the household are affected
• With preliminary treatment: response to previous treatment
• Was itching present first or changes to the skin?

The vet can start to make a diagnosis based on this information and the clinical examination.

Ectoparasites frequently cause itching and are usually easy to detect. These creepy crawlies can be tracked down using skin scrapings, adhesive tape, flea comb tests and swabs. If no parasite is detected and clinical suspicion is still very high, a diagnostic treatment should take place, i.e. a remedy against the suspected parasite is administered and success is awaited.

With the help of cytological procedures or an antibiogram with pathogen detection, we can identify bacteria and yeast fungi as pathogens. Here it is necessary to determine the cause of the colonisation of these infectious agents.

There are also several diagnostic methods for fungal infections (dermatophytes). Examination with a black-light lamp is very simple and a green fluorescence is seen in the hair shaft with positive cases. However, this is only seen in infections with some strains of Microsporum canis, so a negative result doesn’t necessarily mean that no skin fungus is present. A fungal culture can also be created. The material for a fungal culture can be obtained by plucking hairs, scraping skin or the McKenzie method (toothbrush method). Furthermore, a dermatophyte PCR test is available, which is offered by numerous laboratories and hair and skin scrapings are also used as material.

Allergy diagnosis is a tricky challenge. Unfortunately there are no easy and secure tests that tell us which allergy is present. Hence, only a structured allergy reconditioning is diagnostically workable. It’s often relatively easy to diagnose a contact allergy, since itching often occurs quite locally following contact with a certain material or substance. With other allergies, what is known as exclusion diagnosis is useful, i.e. excluding one allergy after another. We start with the most common and generally easiest to diagnose allergy: the flea saliva allergy. Fleas or flea faeces can be found with the help of a flea comb. If no fleas can be found, diagnostic treatment begins for several weeks. If there has been no improvement through repeated and consistent flea treatment, a food allergy is assumed and an exclusion diet is carried out. For a period of at least 6 weeks, the dog should be fed with one source of protein and one source of carbohydrates it has not yet consumed. The body cannot experience an allergic reaction to this food if it has had no prior contact with it. During this period, the dog is not allowed to eat anything else and even its treats should solely be made up of the proteins and carbohydrates from its diet. If itching and other symptoms have improved significantly or disappeared entirely during the diet, the dog should be given the food it previously received. This is known as provocation. Only if the dog now reacts again with symptoms is this proof of a food allergy. If diagnostic treatment and an exclusion diet don’t lead to any improvement, the suspicion of atopy is high. In this case, an intradermal test or serum allergy test to environmental allergens can be carried out to identify the triggering allergens.

If secondary itching is suspected, research into the underlying cause such as hormonal diseases should definitely be carried out, for instance with blood tests including the thyroid levels.

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• Special wet food for dogs with sensitive skin and a tendency to suffer from skin irritations
• Reduced allergen formula thanks to selected sources of protein
• Omega fatty acids to optimally support the care of sensitive skin

Treatment for itching

With extreme itching, it is often necessary to alleviate a dog’s suffering with medication before or during diagnosis. This is possible with rapidly effective medication like glucocorticoids or oclacitinib as well as local treatment, e.g. with shampoos. Nevertheless, it is absolutely necessary to identify the cause of the itching so that the dog can be helped in the long term.

Since ectoparasites are often the cause of itching, the administration of a suitable anti-parasite treatment by the vet is necessary. This treatment takes place after detection of the respective parasites or in cases of very strong suspicion where appropriate. Treating a flea saliva allergy also takes places by regularly administering a compound to combat fleas as well medically reducing itching.

Depending on the severity of a fungal disease, local treatment with ointments or tinctures or systemic treatment with antimycotics may be necessary. However, it should always be taken into account that dermatophytosis is zoonotic and that humans too can be infected. Hence, an environmental treatment may also be necessary in cases of severe dermatophytosis. If itching is severe, it should not be treated with glucocorticoids because they intensify the fungal infection.

Contact allergies are treated by attending to itching and avoiding the allergen. In addition, shampooing with special compounds can weaken allergens on the affected contact points.

If a food allergy is present, it is also recommended to avoid the allergen, i.e. giving food components that the dog tolerates well and doesn’t react to.

The only causal treatment for atopy is hyposensitisation, an allergen-specific immune treatment in which the allergens to which the dog reacts are administered in increasing concentrations in a targeted manner. The objective is to stimulate the dog’s immune system and achieve tolerance towards the allergens that trigger itching. However, not all dogs respond satisfactorily to this treatment. Additional treatment with medication to alleviate itching like cortisone, antihistamines, cyclosporin or oclacitinib is often necessary. Essential fatty acids can also contribute to reducing itching. Another treatment for itching with atopy has also recently become possible: biological treatment with monoclonal antibodies. So far, this type of treatment appears extremely promising and is also very well tolerated.

Secondary infections with bacteria or yeast fungi can be treated with antibacterial or antimycotical local therapeutic agents (shampoos, ointments, sprays etc) or antibiotics and antimycotics depending on the severity. In addition, the causal disease should always be investigated and treated.