Client Resources
Allergic Skin Disease
The skin is the largest organ in the body, and has many complex functions. The skin can be affected by hundreds of different diseases, and allergic skin disease is one of the most common disease complexes we see in dogs and cats in south-east Queensland. How allergic skin disease occurs, the signs seen and how we manage it can vary a lot. Similarly, how our pets respond to treatment and management can also vary a lot, making it also one of the most frustrating chronic conditions for both our pets and their family.
The signs of allergic skin disease can be divided into two categories: the primary signs, and the secondary signs.
The primary signs are the initial effects of inflammation and chemical signal release in response to an allergen. These are often seen as:
- Itching
- Redness
- Warmth (skin can feel hot to touch)
- Swelling (in some cases, not all cases)
Source: Dermatology for Animals Skin & Ear Clinic
The secondary signs are those that occur as a result of persistent primary signs. These are the signs that form part of the cycle of skin disease.
- Rash (raised skin lumps)
- Hair loss (whole areas of the body or just patches)
- Thickened skin
- Pigment changes
- Dry, flaky skin OR excessively oily skin
- Open skin wounds
- Discharge from wounds, ears or eyes
- Odour
A thorough clinical history is key to diagnosing allergic skin disease. Important information is often revealed during discussion with your vet that may not seem like anything significant on its own. Your vet can start to understand whether allergic skin disease is likely to be affecting your pet with information such as:
- What time of year the skin disease seems to occur
- How frequently the skin disease occurs
- Activities prior to the occurrence of the skin disease (e.g. been to the dog park, ran through the back paddock, stuck their head into the garden bushes, floors recently cleaned with a new cleaning product, etc.)
- Types of foods fed and any recent changes
- Types of topical treatments applied (e.g. shampoos or conditioners, lotions, powders, flea treatments, etc.)
Information like this can help your vet to start to piece together the picture why your pets skin is reacting the way it is.
A thorough clinical exam is important in determining which parts of the body are affected and how. Is it just the area that comes in contact with the ground? Is it all over the body? Are there signs of this disease being a chronic, long-term reaction, or are there signs of it being a sudden, acute reaction? Are there other signs that might lead us to consider another disease process?
Some hormonal diseases can cause skin and hair coat changes, and your vet may recommend blood tests to try to determine if these processes are likely to be affecting your pet. Some external parasites can cause significant skin disease, and can be diagnosed by skin scrapings, microscope examinations of hair and/or skin, and other skin examinations during the consult. Sometimes skin disease can occur due to auto-immune disease (the body inappropriately reacting to itself, attacking its own cells), and tissue biopsies are recommended.
Generally, allergic skin disease is diagnosed in general practice based on the clinical history and physical examination during the consultation. However, this diagnosis is often unable to determine what the animal is allergic to specifically. We can usually only determine that the skin disease seen is likely to be associated with allergies, but often not exactly what the animal is allergic to. Veterinary dermatology specialists can provide additional testing options such as skin-scratch tests to try to determine the exact allergen that causes the skin reaction, and referrals are available.
This is a complex question to answer, and is dependent on understanding the likely cause of the skin disease in that individual. Treatment for allergic skin disease is often a combination of reducing exposure to the allergen (if possible), managing the itch and inflammation, managing secondary signs (such as infections), and provide support for the skin to try to maintain its natural barrier function. Many allergic skin conditions need management and treatment in some form for the whole of the animal’s lifetime.
FAD results from a hypersensitivity to flea saliva that comes in contact with the skin when a flea bites and feeds from its host. FAD most commonly affects dogs, and cats are more likely to react to midges or mosquitoes. FAD in dogs often presents as intense itch over the rump and tail, and insect bite hypersensitivities in cats often affect the face and ears (areas with little or no hair). While the allergic reaction process is the same as other allergic skin diseases, management is more focused around avoiding exposure to the bites of these insects. Initial treatment may involve steroids, anti-itch medications, and antibiotics. Long-term treatment for FAD involves a strict flea control plan to minimise the flea burden on the individual dog. For cats, midge and mosquito hypersensitivities may require the cat to be restricted to the indoors, or the application of insect repellents to the affected areas.
Dietary allergies are a very commonly discussed topic with owners at the moment, with the emergence of many new diet options in stores. Grain-free diets are very popular at the moment, with many owners reporting that their pet’s skin appears to improve on theses grain-free diets. The concept of grain-free has been adapted from human nutrition, where grains are often a source for dietary allergies and intolerances. However, the same cannot be said for our four-legged friends. True dietary allergies are actually quite uncommon, seen in less than 1% of dogs. They are slightly more common in cats, affecting up to 6% of cats. The vast majority of dietary allergies in dogs and cats are based on proteins. The most common proteins associated with dietary allergies are beef and chicken, followed by lamb and fish.
That being said, we cannot discount the observations of many pet owners when it comes to their furry friend’s skin and coat. So why is it that grain-free diets seem to help? The theory is that grain-free diets contain higher quality proteins and higher essential fatty acid content. As we discussed earlier, when it comes to the natural skin barrier function, diet can make a big difference. A better quality diet on its own can improve the overall health of the skin and coat, which in turn will reduce the ability of allergens and infections to penetrate the skin barrier and cause an immune response.
True dietary allergies cause skin disease that appears similar to environmental allergies. Unfortunately, unlike people, blood and skin testing can’t diagnose dietary allergies in animals. Instead, we must rely on excluding the likely proteins causing the allergy from the animal’s diet. These are commonly referred to as “food elimination trials”. This can involve feeding a “novel protein”, which is a protein that your pet has never been exposed to before. This can be difficult for a lot of pet owners. The alternative is feeding a hydrolysed protein diet that is commercially produced and recommended by your vet. The proteins in these diets have been treated with enzymes to breakdown the protein into its building blocks that are considerably smaller fragments. These protein fragments are too small for the immune system to respond to, but will still provide the nutrition that the animal needs for a healthy lifestyle. If there is a good clinical response in the animal’s skin and overall condition, then we can consider “rechallenging” their immune system by carefully reintroducing regular proteins back into the diet and monitoring for a skin response. In some cases, the animals do best by simply continuing on the commercial hydrolysed protein diets, and these are designed to be complete and balanced diets for long-term use.