Ear Infections in Dogs
Another reason: dogs have a lot of mast cells that can release histamine and other allergic chemicals.  In other words, it's common for dogs with allergies to have itchy, irritated ears. It all comes together; the allergies irritate the ears and in response they produce more earwax.  Because of the extra ear wax and inflamed ear canals, and because the ear canals in many dogs are extra warm and moist because of anatomy, you can understand why so many dogs keep getting ear infections over and over again.

It's pretty easy to tell when your dog has an ear infection. They shake their head.  They whine. And when you give hugs, you can smell the special odour of a yeasty, bacterial, ear infection. And, of course, if you take a close look, you will see that the ear canal is hot, red, inflamed, and full of goo.  If you touch the ear it will often hurt.  Or elicit groans.  I went to vet school to learn this great stuff.

In case you didn't see my smile, that was a little joke.  But here's something serious.  You can't just assume what I just told you is true ... for your particular pet. Each case is different. Or complicated by other factors. 

Possible other causes include foreign bodies in the ear canal, masses in the ear canal, drug sensitivities, food allergies (which are different from other allergies), thyroid disease, immune disorders, parasites (there are several different types besides the common ear mite), and metabolic disorders including diabetes and cushings disease.  Other factors include "swimmers" ear, excessive hair growth in the ear canals, excessive hair removal from the ear canal, excessive bathing, and sensitivity to harsh earwax cleaners. Oh I forgot to mention yeast and fungus in addition to bacteria.  And sometimes the bacteria are the type that doesn't cooperate and die even when you're using a powerful antibiotic.  Hoo Boy. 

I bring this all to your attention to underscore the importance of a good exam and probably some lab work to try to narrow down all the possible causes.  Your vet will want to have a good look down the ear canal.  It may be necessary to sedate your pet in order to clean out the ear well enough to get a good look.  Or maybe he or she will have you come back after a few days of treatment to look again when hopefully the ear will be improved.

General Comments and Information about Ear Problems
From a treatment and frustration viewpoint, there are 3 types of ear problems... 

1.  Those caused by ear mites.  This is my favourite because it's easy to diagnose and easy to cure.  This is also the most common ear problem in cats.

2.  First time ear problems or pets with a history of occasional ear problems that readily respond to simple treatment, and the ear tissue is normal except for being a little irritated.  These are generally rewarding to treat.

3.  The third type is one we vets frequently have to deal with and are very frustrating to the pet and the owner too.  This is the chronic ear infection that makes the dog miserable and smelly and even though it gets improved with treatment...keeps coming back.  And the ear tissue changes to become thicker, spongier, and more productive...secreting large amounts of inflammatory glaze and goo.

This is a very common problem in dogs, especially dogs with flop ears and/or underlying allergies.

Treatment: (a summary)
Treatment of any under-lying problem that might be discovered

Cleaning of the ear canal.  My favourite product for this in most cases is Zymox.  Often this is all that's needed! 

Application of topical antibiotics and anti-inflammatories

Oral medication if needed.  Antihistamines and/or omega 3 fatty acid supplements are often very helpful.  Oral antibiotics may be needed for deep-seated infections.  Long-term antibiotics are often needed.

As a rule, we try to avoid systemic steroids, at least for long-term use, but sometimes the results are worth the possible problems.  Your vet will talk to you about this if they're needed.

A diet change is not often the answer, but sometimes it's exactly what's needed.  It takes a little bit of intelligent detective work to figure this out.  You can't expect to get success with switching to just any different food.

Repeated cultures are sometimes needed.  There's a bacteria called pseudomonas that's particularly difficult to control and cure.

And finally, sometimes it's necessary to surgically open up the ear canal in order to get long term relief

Some comments about the real problem leading to many chronic ear infections; 

Allergies:
When dogs have repeat ear infections it's often because of underlying allergies.  Here's the deal:  Either flea allergies, food allergies, bacterial allergies, or inhalant allergies (also known as atopy) ...or any combination of these allergies irritate the mast cells that are concentrated in the canals of the dog's ears. 

These are just like the mast cells humans have concentrated in their respiratory system that release histamine, prostaglandins, and other inflammatory chemicals. 

These itchy, inflammatory chemicals released by the mast cells stimulate the glands in the ear to over-produce earwax and other secretions. 

These waxy, gooey ears then become infected by skin bacteria, which thrive in such an environment.  Bacteria does especially well in flop ear dogs where the increased temperature in the ear canal is just right for bacterial incubation because of that cosy flap.

An ear canal with a fermenting vat of skin bacteria and earwax then attracts yeast spores to germinate.  This whole process is very irritating to the ear canals which become thickened, puffy, and ever more productive.

It's a frustrating cycle that often is broken only if you fight off all the main components:  Get the underlying allergies under control.  Get the bacterial infection under control.  Get the yeast under control.  Get the damaged ear canal tissue to heal.

Yeast Infections
Yeast organisms are rarely the primary cause of ear infections, but they certainly are common invaders of ears that are already red, moist, and irritated from other causes.  But once the yeast infection is established it not only makes the ear much more painful and odorous, but it's difficult to solve the ear problem without also treating the yeast problem.  Here's what to expect:

Some vets will diagnose yeast based on the smell and usually be correct.  Other vets will recommend a yeast culture to confirm the possibility.

This bears repeating:  Yeast is rarely the main problem, so expect to also need to treat additional problems.  Just cleaning out your pet's ears with vinegar is NOT likely to be enough.

Treatments:
1.  Diluted vinegar.  Inexpensive and often adequate as a treatment. Vinegar is mildly acetic; yeast doesn't survive well in an acid environment.  Here's the possible problems with vinegar as a treatment:

 a.  Often not successful; probably because the pH change isn't extreme enough or long enough in 
      duration

 b.  Vinegar can sting quite a bit making this a very disagreeable treatment for your pet.

 c.  Vinegar treatments are possibly dangerous as a treatment if the eardrum is damaged.

2.  Zymox.  If you've read much of the rest of this page, then you know I'm a big fan of this product.  It's
     seems to be very effective at treating both bacterial and yeast infections.

3.  Chlorhexiderm products.  Especially the stronger strengths (4%).  Sometimes it's important to
     shampoo the whole dog to get the yeast infection under control.

4.  Other shampoos and topicals that have varying degrees of success at killing yeast.  At our clinic, we've
     been using a  shampoo called "Universal shampoo" that's been working well when we need to treat
     the whole pet and not just the ears.

5.  There are several brands, but many vets sell an ear cleaner/flush that lower the pH of the ear canal,
     which successfully kill the yeast.  These prescription products tend to work better than vinegar
     treatments and are less irritating to the ear canal.                  

Ear Mites
Ear mites are very common in cats but are also seen in dogs occasionally

There are several different types, but in general, like fleas, ear mites have become resistant to most of the over the counter treatments.  Despite the label claims, they simply are not working well. 

Revolution works fairly well at killing ear mites in cats.

Even more effective are topical applications of ivermectin, which you need to get from your vet.  A lot of you know that Ivermectin products are sold for use in livestock and as a heartworm preventive in dogs and cats, but you risk some fairly severe side effects if you apply these stronger products directly into the tender ear canals of cats and especially kittens.