Maybe you can relate to this scenario. It's a lazy Sunday afternoon and I'm laying on the couch watching television. When my two year old Lab, Luke, comes up and plops his had on the cushion near my head. At first, I give him a quick rub around the ears and then it hits. The smell from his mouth was awful.
So, I'm a take action kind of dog owner. I immediately Google "dog has bad breath" and here is what I saw. It was my fault... I wasn't brushing his teeth enough. According to the AKC:
The simplest way to prevent bad dog breath is to brush your dog’s teeth on a regular basis. Teeth brushing reduces plaque and promotes better oral hygiene, much as it does in humans, and with a little training, most dogs learn to enjoy having their teeth brushed.
Providing your dog with plenty of chew toys helps them take care of their teeth naturally. Chewing prevents plaque and tartar build-up and relieves boredom, keeping your dog healthy and happy. Just make sure you select chew toys appropriate for your dog’s size and age."
While I was searching the internet I also found some treats that are worth sharing. Greenies Original Dental Treats. They really helped Luke and selfishly his owner. In case you're curious, I tried to generic version from Costco and they DID NOT work the same.
It's also worth noting that I am not a vet and do not have medical training. Please contact a medical professional for any concerns you may have about your pet.