Allergies and Itchy Dogs
We’ve all seen the look of intense
pleasure on our dog’s face when it itches in just the right
place, and our own casual scratching of a chin or an ear can
elicit a grateful lick or nudge. But sometimes itching
becomes more relentless in our canine friends who are
susceptible to allergies, creating considerable discomfort.
GRRI recently spoke with Dr. Karen
Helton-Rhodes, who specializes in canine dermatological
disorders, to find out more about allergies and how we can
help provide relief.
GRRI: Thanks, Dr. Rhodes, for
agreeing to spend some time with us. All dogs itch from time
to time; what kinds of symptoms should begin to suggest that
there might be a problem with allergies?
Dr. Rhodes: Well, although
allergies are pretty common, we might see some symptoms that
would suggest allergies as one potential problem among a
group of conditions that provoke similar reactions in dogs.
In general we’re looking for things like intense itching,
especially around the feet, face, and axillary (the
“armpits”) regions of the dog’s body. The ears tend be
involved as well, with otitis externa commonly presenting.
If the problem is chronic, we might see thickening and
changing pigmentation in the skin.
GRRI: But you’re suggesting that
these symptoms don’t automatically mean that allergic
reactions are involved?
Dr. Rhodes: No, not necessarily.
Dogs often have other problems, which may be secondary to
symptoms of allergic dermatitis, or may in fact be the
primary problem. For example, we see cases of malassezia in
itchy dogs, which is an overgrowth of yeast. The yeast are
effective opportunists that take advantage of the allergic
dog’s condition; for example, dogs suffering from allergies
will often produce a lot of ear wax which is a good
microenvironment for yeast and bacterial overgrowth. Other
problems that you might see include staph bacterial
infection of the skin and hair follicles (pyoderma), which
would also create itching along with some rash, pimples, or
hot spots. Conditions like a scabies infestation (caused by
a burrowing mite) or a fungal disease like ringworm would
also cause a lot of itching and discomfort.
GRRI: So how do you figure out
what the real problem is?
Dr. Rhodes: Sometimes it isn’t
so easy! There is some testing that we can consider, but
before we discuss that maybe it would be good to think about
the physiological responses a dog has to the presence of an
allergen. Basically any dog, allergic or not, will produce
antibodies in response to the presence of what the body will
consider to be “foreign” proteins. So, whether it is pollen
or mites or a kind of food or mold or whatever, the dog’s
immune system begins to produce antibodies to the “invader”.
We categorize the antibodies as IgE, IgG, or IgM, and what
we think is going on is that allergic dogs produce
significantly higher levels of the IgE category of
antibodies. Some dogs tolerate higher levels of IgE
antibodies better than others.
GRRI: So these IgE antibodies
cause more sensitive dogs to itch?
Dr. Rhodes: Indirectly, yes. The
IgE antibody will bind to mast cells in the skin. When the
dog is exposed to the allergen again, the allergen will bind
to the IgE antibody attached to the mast cells. This binding
of the allergen will cause the mast cell to rupture,
releasing chemicals (histamines, leukotrienes,
prostaglandins, etc) that cause the skin to itch.
We can try to look for the specific
kinds of IgE antibodies produced for each allergen in the
dog’s blood; this is often referred to as in vitro testing,
or serum or plasma testing. There are two general techniques
for serum testing, one using a radioactive tag (“RAST”) to
identify the appropriate antibody, and another using an
enzyme (“ELISA”) tag . Serum testing is fairly easy and not
that expensive, but I don’t usually recommend it because it
suffers from poor reproducibility in tests and is
susceptible to too many false positives; that is, the test
indicates an allergy to a substance that doesn’t in fact
provoke the problematic response. I certainly wouldn’t use a
serum test for a suspected food allergy; a trial elimination
diet is the only way to find the offending food.
GRRI: So you’d feed the dog
only a simple diet of what you know wouldn’t cause the
allergic reaction, and gradually add things until you saw
the allergic response?
Dr. Rhodes: Exactly.
GRRI: How could you tell at the
onset of the itching if it was caused by a food allergy or
allergy to something else?
Dr. Rhodes: You really can’t; I
told you this wasn’t easy! We used to think that food
allergy symptoms were focused more on the head and ears, but
over the years we’ve come to observe that this isn’t
necessarily true. If the dog had gastrointestinal symptoms
along with the other symptoms of allergies, we might think
about food allergies first. What’s happening in those cases
is that mast cells bound to allergens passing through the
gut are rupturing, releasing the same irritating chemicals
that promote itching in the skin.
Our usual approach is to try to look
for the secondary problems like yeast or bacteria and treat
them, and also rule out things like mites or fungal
infections. If the symptoms didn’t change with the season,
we’d start a food trial to try to identify the allergen.
Seasonal symptoms might point us more towards an allergy
resulting from inhalation or contact with something.
GRRI: What about skin tests?
Dr. Rhodes: Intradermal skin
testing is considered the “gold standard” of allergy
testing. We can inject between 50 and 80 allergens into the
skin, and then measure the response of the skin to identify
problems with specific allergens. One possible disadvantage
to intradermal testing is that there needs to be between 2-8
weeks of abstinence from use of a variety of drugs that may
interfere with the dog’s immune response. So, if a dog were
being treated with these kinds of drugs for some condition,
they would need to stop using the drugs for some time, which
isn’t always feasible. For an itchy dog, it is tough to
pull them off the drugs that are making them comfortable;
the good news is that one effective therapy for itching
(cyclosporine) does not need to be terminated before a skin
GRRI: Can we take a shortcut
here? Are Golden Retrievers particularly susceptible to
specific types of allergens?
Dr. Rhodes: We don’t see any
evidence of that. We do think there is genetic
predisposition to allergic dermatitis in Goldens, but it
isn’t specific to a particular allergen. That said, I’d note
that house dust and dust mites are very common offending
GRRI: Most of us are so happy
just to get rid of the clumps of dog hair floating around
our houses that we don’t always get to dusting. If it is
inevitable that a dog will come into contact with an
allergen like dust, how can we treat the problem?
Dr. Rhodes: We have a couple of
options. Hyposensitization is a way of trying to induce
immunological tolerance by injecting small doses of the
allergen over an extended period of time. It is similar to
the thinking behind vaccination. Most dogs tolerate the
injections very well, and people get used to administering
the injections pretty quickly. It isn’t a cure, but
hyposensitization is a very reasonable way of managing the
problem over the longer term. The disadvantage here is that
it may take many months before you begin to see relief, as
the sensitization process is a pretty slow one.
We also have a variety of drugs that
may relieve symptoms. Antihistamines seem to be effective in
about 50% of allergic dogs; the challenge is to find the
right drug for each particular dog. Typically we have our
clients begin trials of over-the-counter antihistamines,
with the idea being to observe the dog’s reaction for a week
or two before deciding on its effectiveness. If
over-the-counter drugs aren’t useful, we can move on to some
prescription antihistamines. If those aren’t helpful, we’ve
had a lot of success with a drug used in human organ
transplants to help reduce organ rejection; cyclosporine
works well and doesn’t have some of the negative side
effects of corticosteroids, but unfortunately it is quite
GRRI: What about nutritional
Dr. Rhodes: Well, the data is a
little soft, but there is at least some evidence that
essential fatty acid supplementation may be helpful in about
25% of the cases. The EFA’s act as an anti-inflammatory, and
since there isn’t any harm in supplementing a dog’s diet
with them other than the expense, I’d certainly try it.
GRRI: How about the sprays or
creams we see for itching?
Dr. Rhodes: We will often
suggest use of a spray that has a very low dose of
triamcinalone, which provides temporary relief of severe
itching. Many of our patients are on a regular shampoo
regimen as well, which is especially effective at addressing
some of the coincident problems like yeast or bacterial
infections that we talked about earlier. It really is
amazing what a difference something as simple as a Selsen
Blue shampoo two or three times a week can make in those
GRRI: It sounds as if we have
at least a couple of good options to relieve the discomfort
that allergies can cause. Dr. Rhodes, thanks so much for
speaking with us.
practiced as a board-certified veterinary dermatologist in
the tri-state area since 1982. As head of the department of
dermatology at the Animal Medical Center in New York for 12
years, she actively participated in the training of the
interns and residents. Dr. Helton-Rhodes also held the
position of Assistant Clinical Professor of Dermatology at
New York University Hospital from 1985 until 1997. This
position facilitated communication and research
opportunities in the area of comparative dermatology. She
received the Merit Award from VMA of NYC in 1991, Clendenin
J. Ryan teaching award in 1992 and was honored by being
listed as one of the “Best Veterinarians in New York” by New
York Magazine in 2002. In 1994 she joined a specialty group
in New Jersey, Animal Emergency and Referral Associates. As
the practice grew, Dr. Helton-Rhodes developed an affiliate
practice, Veterinary Referral Centre, located in Little
Falls, New Jersey as the primary location of her referral
Helton-Rhodes has lectured extensively on the topic of
veterinary dermatology, allergy, immunology and
dermatopathology. She is the author of numerous textbook
chapters, medical journals articles, and has authored a
veterinary textbook entitled "The 5-Minute Veterinary
Consult: Clinical Companion in Small Animal Dermatology."