What Causes Bad Breath in Dogs?

Pond scum. This is the stuff that sits on the top of the water on ponds, puddles or swamps where the flow of water is not very good. This pond scum is usually a green to brown colour, it is a living community of all sorts of nasty things like bacteria, algae and protozoa and like all communities it grows as large as possible. Oh, and it smells bad. If you walk through the water the scum sticks to you and is hard to get off and very quickly you smell like the stagnant pond.

Pond scum with all the living organisms in it is considered a “biofilm”.  Biofilms are communities of different living organisms all stuck together by mucus they produce. This mucus ‘floats’ on top of whatever the biofilm sticks to.

So, what does all this have to do with teeth? We have and our pets have biofilms in our mouths. This biofilm of the mouth is called ‘plaque’. Plaque biofilm is filled with all sorts of bacteria and other organisms all living in a slimy mucus which sticks to teeth really well.  Like pond scum, when plaque biofilm gets on other things the bad smell comes with it. When our pets clean themselves (or lick us) this transfer of plaque biofilm full of smelly bacteria makes their fur or our hands smell like dirty mouths. Yuck.

The bacteria and other inhabitants of the biofilm are not very responsive to antibiotics, sprays or water additives. Mouth washes we use help to keep bacteria levels down but it is tough to teach dogs and cats to gargle. The most effective way to remove the ‘pond scum’ or plaque biofilm  from teeth is to brush it off; either with a toothbrush or some mildly abrasive material. This physically removes the plaque and all the associated smell-producing bacteria. This helps reduce smell in the mouth, keeps the mouth more healthy and prevents the formation of tartar. The most disappointing aspect of brushing off the plaque is that, as soon as we do this, new plaque starts to form. This is why we need to brush every day.

In ponds, when the pond scum covers the whole water surface, it kills everything in the pond. When plaque is allowed to grow unbrushed in a mouth, it eats away at the tissues holding the teeth. Eventually the plaque bacteria kills all the teeth and they fall out or have to be removed. In both ponds and mouths it is best to keep the biofilms (pond scum and plaque) away and this allows the ponds and our pets’ mouths to stay healthy.

Brushing removes plaque biofilm and keeps our pets healthy with mouths smiling.

By : Dr. David Kerr, DVM


Dog looking out the window

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Last updated: December 16, 2020

Dear Clients,

With recent changes to restrictions on businesses, we are pleased to advise that effective May 19, 2020 some restrictions on veterinary practices have been lifted. Based on these changes, below are some important updates to our operating policies.


This includes vaccines, wellness exams, blood work, heartworm testing, spays and neuters, dental services, and more!



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Thank you for your patience and understanding and we look forward to seeing you and your furry family members again!

- Your dedicated team at North Hill Animal Hospital