The science behind Fido's funk
In this short video, the American Chemical Society breaks down the cause of wet dog smell, that funky odor that dogs have, particularly when they are wet, or when they have not been bathed in a long time.
In humans, body odor is mainly caused by sweat. Bacteria and yeast digest the sweat and release bacterial smells. But dogs, of course, only sweat on their feet (and their nose, to a lesser extent).
However, bacteria and yeasts also live in your dog's coat. Most of the time they silently lurk there, not causing much of a fuss. Like the organisms on humans, these bacteria and yeast excrete volatile compounds (stinky smells) as part of their digestive process.
When a dog's coat is dry, the volatile compounds tend to stick to the fur. But when the coat becomes wet, the dampness releases the odors, "activating" the smell.