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Dr.Beth, Dog Veterinarian
Category: Dog
Satisfied Customers: 631
Experience:  Doctor of Veterinary Medicine, University of Minnesota
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My dog has a black spot on his tail. Been there for months

Customer Question

My dog has a black spot on his tail. Been there for months now. My vet perscribed antibiotics a while back but it did nothing. I think he called it a fox tail (I could be wrong on that because those are the thorns they get in their paws and I know it's not the same thing) but there was a term he used. It doesn't seem sensitive at all for the dog or seem to bother him, but it is kind of ugly. Any ideas?
Submitted: 7 years ago.
Category: Dog
Expert:  Dr.Beth replied 7 years ago.
I often see this kind of spot on the tails of dogs that have Hypothyroidism (low thyroid levels). The tail will have an area of hair loss, the skin will turn a black color and it is not itchy or painful for the dog. You will need your vet to run a T4 and TSH blood test to diagnose this condition.

Other possible causes that should be ruled out would include a fungal infection (like ringworm) and a mite infection (like Demodex). Your vet can test for these infections as well.

The final cause that I see sometimes in large breed dogs, is that this is similar to a callus. If your dog tends to fold its tail under and sit on it (especially on hard or rough surfaces), this habit will cause hair loss and the skin to toughen into a callus in the area.

Please let me know if I can be of further help.

Dr. Beth

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