Allegric Skin Disease

Allergies and hypersensitivities are a disorder of the immune system. The immune system in pets is designed to defend the body against harmful pathogens.

However, in our allergic pets, after exposure to certain stimuli or substances, the immune system overreacts, producing an undesirable immune response to certain allergens that would be considered harmless in a non-allergic animal.

This allergic response, or hypersensitivity, can manifest as itchy, red and inflamed skin.

There are four common allergic skin diseases that our pets can be diagnosed with. These are:

  • Flea Allergy Dermatitis
  • Atopic Dermatitis
  • Allergic Contact Dermatitis
  • Cutaneous Adverse Food Reaction

Clinical signs for each of these diseases can be very similar and sometimes there can be an overlap of diseases, where your pet may have two concurrent allergies, for example Flea Allergic Dermatitis as well as Atopic Dermatitis.

The following sections below will elaborate on each of these four common allergies.

Whilst allergies are a common cause of skin disease, there are many other diseases that can also cause itchy, red and inflamed skin.

Along with taking a history and performing a clinical exam, your veterinarian may also perform skin tests to rule out these other causes.

Flea Allergy Dermatitis
Flea Allergy Dermatitis (FAD) results from an allergy to a protein in the flea saliva, that comes into contact with the pet when they get a bite from a flea. Dogs and cats with FAD often have a low flea burden. This is because after repeated exposure to the flea saliva, the animal can develop a hypersensitivity to the saliva which can result in a severe skin reaction even after one bite from a flea. In dogs and cats that do not have FAD, they can often have a high flea burden with minimal signs or symptoms of clinical disease. However, in animals with FAD, even a few fleas can cause severe itching.

Dogs can develop red irritated skin with hair loss, primarily concentrated over the rump, tail base and thighs. They are also extremely itchy. Cats may also be affected around the head and neck. Often these animals will cause a lot of self trauma through biting, chewing, scratching and rolling. Secondary infections are common.

A diagnosis of FAD is usually based on the location of skin lesions and the itch resolving after a flea control trial. While evidence of fleas or flea “dirt” (faeces) can help with the diagnosis, they are not always easy to find, especially in cats who groom themselves well.

Flea Allergy Dermatitis is best managed by ensuring the pet is on regular flea prevention, and that the pet’s environment has been treated for fleas. All other in contact pets, or pets in the same household, should also be put on a regular flea prevention programme as this will help to minimise exposure.

If you suspect that your pet has fleas or is suffering from Flea Allergy Dermatitis, contact your veterinarian to discuss the most appropriate flea control plan for your pet.
Atopic Dermatitis
Canine Atopic Dermatitis is a genetically predisposed allergic skin disease and is one of the most common inflammatory skin diseases in dogs. The pathogenesis is complex and is continuously being updated as we learn more about this disease.

These dogs are allergic to environmental allergens such as dust mites and tree pollens. These types of allergies, if involving plant pollens, are commonly seasonal due to timing of pollination throughout the year.

Exposure to these allergens is via inhalation or absorption through the skin. Once the animal has had exposure to the allergen, they will mount an exaggerated immune response and develop clinical signs such as itching and inflammation of the skin. Animals with Atopic Dermatitis will scratch, chew, lick or rub areas of the body such as their paws, face, ears, axillae (armpits) and abdomen. The location of the itch can vary between animals and the severity of the itch can vary also. Some animals may only display itchy ears while other animals may suffer from severe itching in many different locations of the body.

A diagnosis is made by ruling out other causes of itching, such as parasites, food allergy, and contact allergy as well as bacterial and fungal infections. The history of the pet’s itching and the sites of itching are assessed by your veterinarian to ensure that they fit with a diagnosis of Atopic Dermatitis.

Once a diagnosis has been made, an allergy test can be performed. The aim of the allergy testing is to identify which environmental allergens the animal is allergic to, not to diagnose the presence of Atopic Dermatitis. The allergy tests that are most useful for Atopic Dermatitis are intradermal skin tests or blood tests. Once the allergens have been identified via testing, desensitising vaccines can be prepared for that animal.

Desensitising vaccines are the only treatment choice which alter the animal’s immune response to benign environmental stimuli. These vaccines aim to desensitise your pet to the specific allergens by giving controlled amounts of the vaccine via an injection or orally under the tongue. Over time, after receiving regular doses of the vaccine, your pet’s immune system will become desensitised to the allergen and will not mount an exaggerated immune response when exposed to the allergen in normal conditions.

There are many other medications and treatment modalities that we can use in pets with Atopic Dermatitis and sometimes a combination of these are required to control and manage this complex disease.
Contact Allergies
Allergic Contact Dermatitis is an inflammatory skin condition that occurs when your pet comes into direct contact with a substance that they are allergic to. As this is an allergic response, usually the substance that the pet is allergic to is otherwise harmless in normal pets. In contrast, Irritant Contact Dermatitis is an inflammatory reaction to a substance which is known to be an irritant. As our focus is more about hypersensitivities, Allergic Contact Dermatitis is what will be discussed in this section.

The most common allergens are plants such as “Wandering Trad” and “Moses in the Cradle”, however other substances such as cement, floor polishes and carpet deodorisers have been shown to affect pets as well. Because this type of allergy requires direct contact between the skin and the offending substance, usually only sparsely haired areas, which are in contact with the ground, are affected. When very hairy areas are affected with dermatitis, we are less suspicious of contact dermatitis.

Common symptoms include red, inflamed bumps (macules and papules) which can be very itchy. The affected areas can include the abdomen and underside of the chest, underneath the tail, front of the neck and chin and the inside of the ear pinnae (ear flaps). Over time, these lesions may spread to involve larger areas as hair loss progresses in nearby areas. Depending on the offending substance, clinical signs may be seasonal or non-seasonal.

A diagnosis of contact dermatitis is made by combining information from the pet’s history with observation of the location of the skin lesions and demonstrating that the clinical signs resolve when the pet is isolated from possible allergens. To maximise the effect of the isolation trial, we usually recommend that the pet is first bathed with a gentle, hypoallergenic shampoo to remove possible allergens. A “patch test” can also be performed by your veterinarian which involves applying the suspected allergens to the skin and seeing if a localised reaction occurs. This can help determine which plants or materials are likely to be the cause of the contact dermatitis.

Once diagnosed, management of these cases relies on avoidance of the allergens. However, this may not be possible in every case and topical anti-inflammatory medications can be useful as part of the management. In more severe cases systemic anti-inflammatory and anti-itch medications may be required.
Food Allergy
Cutaneous Adverse Food Reaction (CAFR) is caused by an allergy to a component of the pet’s food. The food allergies tend to be towards the proteins present in food. In dogs, the most common food allergies include beef, chicken, dairy products, wheat and lamb. In cats, allergies to beef, chicken and fish are most common. Usually there is prior exposure to the particular food in order to develop an allergy to it. This means that the food allergy will likely be something that has been in your pet’s diet for a while.

Clinically, Cutaneous Adverse Food Reactions are difficult to distinguish from other types of allergies, such as Atopic Dermatitis. CAFR is recognised as a potential cause of non-seasonal itching and occasional gastrointestinal signs in dogs and cats. The clinical signs that you might see with CAFR are very similar to Atopic Dermatitis. The distribution of lesions and areas affected may range from just ear inflammation to whole body itching. Some pets may have concurrent gastrointestinal signs such as vomiting, diarrhoea, flatulence or even increased toileting habits. A common presentation in cats is itching around the neck and face, however it can also be generalised.

Similar to Atopic Dermatitis, these patients are very prone to secondary bacterial and yeast infections. The presence of these secondary infections can complicate reaching a definitive diagnosis and can make management more difficult.

Food allergies cannot reliably be tested for with blood tests. To determine whether a food allergy is present, an elimination diet trial must be performed. This consists of feeding your pet either a hydrolysed diet from your veterinarian, or a home cooked diet that contains ingredients that your pet has not had previous exposure to (a novel diet). The trial should be continued for 8-12 weeks, or as advised by your veterinarian. When doing a food trial, you may need to discuss with your veterinarian alternative non flavoured parasite prevention to avoid possible contamination with a food type that you are trying to avoid.

At the end of the 8-12 week period, if the itching stops, your veterinarian will guide you through reintroduction of your pet’s previous diet to identify the cause of your pet’s food allergy. A diet that avoids the specific allergen can then be chosen for long term use. It is important that the long term diet chosen for your pet is a complete and balanced diet.

The prognosis for CAFR is good once the food allergen has been identified and can be avoided. Occasionally, animals may experience further dietary intolerances and may require repeat elimination trials, as they can over time become intolerant to other foods.

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