This is one of the few behavior questions where veterinary behavior guidance is close to unanimous, and where the common household instinct points the wrong way.
What a growl actually is
A growl is a request for distance. It is not a bid for status and it is not defiance. It sits near the top of a ladder of quieter signals the dog has usually already tried: turning away, freezing, lip licking, showing the whites of the eyes.
By the time a dog growls, they have generally already asked politely and been ignored. That is worth knowing, because it reframes the growl from rudeness into persistence.
Why punishing it is the specific problem
Punishment may suppress the growl without changing the fear, pain or conflict behind it. That can make the dog's later behavior harder to read while the original problem remains.
That is the origin of a great many dogs described as biting without warning. The warning was removed on purpose, by someone who meant well. The AVSAB position statement on humane training sets out the broader evidence that aversive methods carry a risk of increasing fear based and aggressive behavior rather than reducing it.
What to do instead, in order
- Stop. Move away, take the pressure off, end whatever was happening. This is not rewarding the growl; it is answering it.
- Write down what was happening immediately beforehand. Who, where, what was being touched or approached, what the dog had.
- Change the setup so the situation stops recurring while you work out the rest.
- Book a veterinary examination, particularly if this is new.
- Get qualified in person help for anything involving a bite, children, or a pattern that is widening.
If the reaction followed several smaller stresses or exciting events, review trigger stacking in dogs. That term can help organize what happened earlier without excusing unsafe behavior or replacing an individual behavior plan.
The medical part people skip
A dog who has always tolerated having their ears handled and suddenly growls when you reach for them is more likely to have a sore ear than a new attitude. Dental pain, arthritis, ear disease and abdominal discomfort all show up first as reduced tolerance for handling.
Merck's table of medical causes of behavioral signs is a reasonable illustration of how wide that list is. Any behavior change that arrives suddenly in an otherwise settled dog deserves a physical examination before a training plan.
A note on thanking the growl
You will see advice to be grateful for a growl. It is well meant and broadly right, but it is easy to misread as doing nothing. Being glad of the warning and then continuing to do the thing that caused it is worse than either option alone, because it pairs the warning with being ignored anyway.