Keep an eye on it
What it can look like. A general, vet-reviewed example — signs vary and this is not a diagnosis. When in doubt, ask your vet. 
Ear discharge & odor in dogs
Clinical name: Ceruminous / purulent otitis
Waxy, brown or yellow discharge with a yeasty or sour smell.
Where it shows upears
Typical patternEar canal.
Linked allergy typesEnvironmental (atopy) · Food allergy
Food vs environmentalNon-specific.
What you can do
Don't poke cotton buds deep; have a vet look and swab it.
Don't confuse it with
Other causes a vet will want to rule out: ear mites, yeast overgrowth.
This is educational information, not a diagnosis or treatment plan. Always see your veterinarian about your dog's health.
Related signs
Recurring ear infectionsSee your vet
Red, swollen, sometimes smelly ear canals with discharge.
Head shaking & ear scratchingKeep an eye on it
Repeated head shaking and pawing or scratching at the ears.
Swollen ear flapSee your vet
A soft, fluid-filled swelling of the ear flap, caused by violent head-shaking.