As discussed in Allergies in Dog Causes, allergens can be categorized in a variety of ways; route of exposure, symptoms produced or allergen source are but a few of the possibilities. The umbrella term ‘Environmental allergies’ encompasses an extensive range of substances (environmental allergens) found in one’s surroundings that act as allergy triggers/irritants.
Most Common Type of Allergy in Dogs – Environmental Allergies
It is believed that environmental-related allergies are the most common type of allergic disease in dogs. Although estimates vary depending on one’s source of data, allergies account for up to 25% of all visits to a veterinarian; approximately 80% of these can be categorized as environmental allergies. Around 50% of dogs with allergies will experience ear-related problems e.g. severe inflammation of ear flaps, lesions or possible infections.
Common examples of environmental allergens include chemicals, dander, dust, dust mites, grasses, metals, mold, pollens, trees and weeds. These substances can be sub-categorized in various ways. For example:
- Seasonal (e.g. pollen) or non-seasonal (e.g. dust).
- Outdoor (e.g. ragweed) or indoor (e.g. furniture fabric such as wool).
As a rough guide, outdoor allergens are often seasonal whereas indoor allergens are all-year-round, however there are many exceptions to this rule.
- Route of exposure. A dog can be exposed to environmental allergens via inhalation, contact or ingestion.
As a group, inhalation allergies (sometimes referred to as atopy or atopic allergies – see below) represent the most common cause of allergies in dogs; dust/dust mites are typically considered the most common inhalant allergen problem in dogs. However, Arlian et al.2003 suggested that sensitivity to storage mites (present in dry foods, grains, cheese etc.) “may be as important, if not more important, than dust mite sensitivity” in dogs.
Furthermore, the route of allergen exposure and allergy development tendency may be linked. For example, seasonal inhalant allergies e.g. to pollen, tend to appear earlier in dogs (70% of cases develop at 1-3 years of age) when compared to the onset of food allergies (typically 3-4+ years old).
Environmental Allergies and Atopy/Atopic Allergies
The precise role played by nature (hereditary factors) and nurture (non-hereditary factors) in allergies triggered by environmental allergens is currently not fully understood. However, as noted in Nature, Nurture and Allergies – A Complex Condition, the term ‘atopy’ and therefore ‘atopic allergies’, refers to a genetic predisposition to Type 1 Hypersensitivity involving IgE following allergen exposure; in particular to environmental allergens.
Unfortunately, the meaning of the terms atopy/atopic allergies varies considerably between sources which can be rather confusing to the reader. For example, atopic dermatitis – which will be discussed later – is still sometimes referred to as atopic eczema or atopy and even by its former name, allergic inhalant dermatitis. As noted in Allergic Skin Conditions, being aware of the historical context helps our understanding of the situation:
“atopy was synonymous with skin allergies caused by inhalant/airborne allergens e.g. dust, pollen. However, it has since been shown that allergens entering the body by other modes i.e. contact or ingestion, can trigger a range of symptoms (including skin conditions) both locally and at distant locations around the body.”
Therefore, in the context of atopy/atopic allergy, ‘atopy’ represents the predisposition or tendency for allergy development whereas ‘allergy’ implies actual symptom development following allergen contact. Despite an individual having a genetic predisposition (inherited genetic trait) to a particular allergy, numerous factors (e.g. gene variability, exposure profile etc.) appear to determine the outcome. Outcome in this context refers to the type, frequency and severity of allergy symptoms, or whether an individual will ever go on to develop symptoms.
Most Common Allergic Skin Conditions in Dogs – Flea Allergy Dermatitis and Atopic Dermatitis
Dermatitis is a general term that refers to skin inflammation usually associated with external irritants or allergic reactions. Skin problems and itchiness are probably the most commonly reported symptoms of allergies in dogs. In fact, skin allergies and related infections typically rank 1st or 2nd concerning dog insurance claims, whereas gastrointestinal problems of an allergy/non-allergy origin usually compete for top spot.
The two most common allergic skin conditions are:
Flea Allergy Dermatitis (FAD)
Not only is an allergy to fleas considered the most common allergic skin condition affecting dogs but many sources list it as being the single most common cause of canine allergies; up to 40% of dogs may be affected by the problem.
Fleas feed on blood by puncturing the skin and tapping into the underlying dermal network of blood vessels. An allergic reaction may be mounted by the canine immune system in response to the ‘soup’ of antigenic material (15+ allergens) present in flea saliva. A single flea bite is enough to trigger events in a predisposed individual; an estimated 80% of dogs with flea allergies have no trace of fleas on them when examined.
Flea allergies most commonly reveal themselves in younger dogs between 1-3 years of age (60% of cases) although they can occur at any age. The classic symptom profile is severe pruritus developing within a triangular-zoned hind region of the dog; from the middle back to tip of tail and rear legs.
Atopic Dermatitis (a.k.a. atopic eczema, atopy and formerly allergic inhalant dermatitis)
Canine atopic dermatitis is considered to be the second most common dog allergic skin condition; approximately 10-15% of dogs may be hypersensitive in this way. Moreover, it is frequently listed as being the single most common contributor to ear infections in dogs.
Females seem at greater risk as do certain allergy-prone dog breeds e.g. Cairn Terriers, Labrador Retrievers and Shar Pei. Severe inflammation and pruritus lesions are commonly associated with the face/muzzle, feet and abdomen and excessive scratching and self-trauma can lead to infections/secondary infections in these areas. Associated signs include loss of hair (alopecia), discoloration (hyperpigmentation) and staining of coat from excessive licking, chewing and nibbling.
The most common environmental allergen trigger of atopic dermatitis is believed to be household dust and dust mites. Support for this comes from a number of research studies, for example:
Masuda et al. 2000, a Japanese canine atopic dermatitis study, utilized both in vivo (INV) (intradermal skin test) and in vitro (IVT) (antigen-specific IgE assay) testing. They found:
- Most common allergen trigger was household dust mites (69% INV/ 54.8% IVT) followed by Japanese cedar pollen (50% INV/16.7% IVT). The latter result highlights the notion that significant allergens for atopic dermatitis vary geographically.
- Less than 20% of dogs sampled tested positive to molds or foods.
Zur et al. 2002 retrospective study of canine atopic dermatitis found that:
- Most common allergen trigger was household dust mites (particularly in the fall) followed by molds (particularly in spring and fall). Summer/fall yielded more positive reactions to weeds.
- Reactions to molds/trees/cultivated plants typically triggered skin and ear yeast infections; cultivated plants frequently triggered otitis external (chronic inflammation of a dog’s external ear canal) and pedal (foot) lesions.
Food Allergies in Dogs
It has been estimated that food allergies account for 10-15% of allergies affecting dogs, although some sources place the figure nearer 20%. However, Verlinden et al. 2007 noted,“The exact prevalence of FA [food allergies] in dogs and cats remains unknown.” In addition, 20-30% of dogs with food allergies have other existing allergies (concurrent allergies).
Around 75% of food allergies are protein-related with the majority of the rest being carbohydrate-related. Between 65-80% (depending on data source) of food allergies are attributable to beef, dairy and wheat allergens. Diagnosis will involve undertaking an elimination diet (food trial) and subsequent preventative strategies involve avoiding identified food allergens.
Unlike both flea allergies and seasonal inhalant allergies, which typically reveal themselves within the first three years of a dog’s life, food allergies tend to develop in dogs around 3-4 years or older. However, they can start at any time if the allergenic ingredient is present; food preparation or cost of the food product is immaterial. Factors such as poor storage issues (associated with mites) or food fillers/preservatives/additives can play a role in increasing the risk of certain food allergies.
A food allergy differs from a food intolerance in a number of ways. Food allergies have varied symptoms which can impact various organs/systems (e.g. respiratory, skin and rashes/itching with associated sneezing and wheezing, face rubbing, head shaking, excessive licking, chronic red inflamed feet or ear infections etc.) as well as cause possible gastrointestinal upset e.g. diarrhea, vomiting. Of particular importance is the fact that a food intolerance does not involve an immune system reaction whereas a food allergy does. Verlinden et al. 2007 stated that, “Type I, III, and IV hypersensitivity reactions are the most likely immunologic mechanisms” for food allergies.
