Having an itchy dog can be wearing for you, especially if he’s in the bedroom scratching all night — but think how much more tiring it is for the pet!
Around 1 in 10 dogs is predisposed to allergic skin disease, although that figure is lower in cats. House dust mites are one of the most common pet allergens, with about 30% of dogs who have allergies reacting strongly to their presence.
Other allergens include grass, flower or tree pollens, molds and sometimes even the proteins found in food. When the dog comes into contact with the allergen, the immune system overreacts and releases chemicals that lead to itchiness. Signs of this are skin irritation such as excessive licking, chewing or scratching.
You can think of pet allergies in terms of hay fever in people, except instead of a runny nose and sneezing, the pet becomes itchy.
This leads to licking, chewing and scratching, and eventually this causes skin thickening (so-called “lichenification” because the skin loses its supple texture and takes on the appearance of rough lichen) and hyperpigmentation (the trauma of constant licking makes the skin produce dark pigment as a defense mechanism).
Pets are commonly most itchy on their paws, groin, armpits, face and tummy — everywhere, in fact, except for their backs! There is a genetic component to allergies with affected animals being programmed from birth to become sensitized in the presence of allergens. Most commonly the pet starts to shows signs between 6 months to 3 years of age.
A dog with atopy will have inherited a tendency to have sensitivity from his parents.
However, the first time he encounters an allergen, he will not react; it takes repeated exposure, with the immune system becoming increasingly aroused by the presence of something it regards as foreign, for the itchiness to develop.
Thus, a dog with a food allergy may have been perfectly fine on his regular diet for weeks, and a gradual intolerance developed with repeated exposure.
The vet will have a shrewd suspicion of allergy if the itchiness has a seasonal pattern (dogs with allergies to pollens and grasses are much worse in the summer months). If the dog’s problem goes away in winter and gets worse each summer, this is useful information.
It is tricky to pin down a diagnosis of allergy because biopsies and such only show there is skin inflammation rather than tell the clinician the cause.
Intradermal skin tests are notoriously unreliable in cats, and in dogs the size of the reaction may not necessarily correlate to the severity of the itch.
It is, however, sensible to rule out as many causes of skin disease as possible by doing skin scrapes to look for parasites and biopsies to check for ringworm, autoimmune skin disease and cancer.
Treatment can be complicated by secondary bacterial skin infections that make the skin itchier, so in the first instance, cleansing shampoos and antibiotics are prescribed to improve skin health.
If the dog is very itchy, a course of corticosteroid is highly effective at settling inflammation. In the longer term, other anti-inflammatory drugs are available that have fewer side effects (but take longer to take effect, hence the importance of making the pet comfortable with steroids).
In this video, Dr. Fawcett of Sydney Animal Hospitals explains treatment options to help pets:
House dust mites are a potent allergen, and regular cleaning with a vacuum that has an allergen filter is highly recommended. Many allergens are absorbed through the skin, so regular bathing of the pet in the pollen season can decrease the amount of allergen in contact with the skin.
Around 30 to 40% of pets with allergies respond well to bespoke immunotherapy vaccines developed for the individual animal. These are developed using the allergen to which the pet is sensitive, and the pet is given small but increasing doses of vaccine with the aim of desensitization.
- “Atopic skin disease — a review and a reconsideration of diagnostic criteria.” Willemse. JSAP, 27: 771–778.
- “Long-term management of atopic disease in the dog.” Bevier. Vet Clin North Am, 20: 1487–1507.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Dec. 19, 2014.