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John Taylor
John Taylor, Dog Veterinarian
Category: Dog
Satisfied Customers: 106
Experience:  MA VetMB MRCVS
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I noticed a large hard knot under my dogs skin on his back

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I noticed a large hard knot under my dogs skin on his back towards his right hip. There was a scabby area in his hair so I shaved the area to get a better look. As I was scratching off the scabby residue, it suddenly erupted with pus and a black granular discharge. He didn't appear to be in pain and as I massaged the knot gently, I was able to work out a substantial amount of the black stuff; however, it wasn't always grainy. It was oily and more solid...almost like a black head in people. It continued to alternate between pus, black grainy discharge, and this solid oily black substance until the knot was all but gone. The next day, I checked it and it had a little more pus and clear fluid but now, a few days late, there is no knot and only a small scab remaining. Should I be concerned or did my dog just basically have a pimple?

This sounds like it could have been an abscess, though this is generally painful, or more likely a sebaceous cyst:
(apologies for pop-up, it's otherwise a good site)

They're generally not a problem but can fill up again. It's great that it seems to have resolved; keep a close eye on it and if it becomes infected or painful then you should get it checked out to make sure there's nothing more sinister behind it.

Good luck

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