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.
Hair loss / thinning in dogs
Clinical name: Alopecia
Thinning or bald patches, often from self-trauma rather than the hair falling out on its own.
Where it shows upflanks · legs · eyes · rump
Typical patternFlanks, legs, around the eyes, and the rump.
Linked allergy typesFlea allergy · Environmental (atopy) · Food allergy
Food vs environmentalRump/tail-base hair loss leans flea allergy.
What you can do
Note whether it's symmetrical or where your dog licks most.
Don't confuse it with
Other causes a vet will want to rule out: mange, ringworm, hormonal disease.
This is educational information, not a diagnosis or treatment plan. Always see your veterinarian about your dog's health.