Reader Question: Recurring, Bleeding Lump on Dog's Leg — What Could It Be?

by Diana
(Sacramento)

Question: This infection on my dog's leg showed up a month ago, healed over and hair grew back, suddenly emerged again a week ago and getting larger and bleeding.

Recurrence of Infection on Dog's Leg

Hi Diana,

Thanks for sending the photo along — it helps a lot. Looking at it, I see a raised, moist, reddish-pink area with some glistening, almost cauliflower-like texture, surrounded by a hairless rim on what looks like the back of the leg. I want to be direct with you: the pattern you're describing — a spot that fully healed with hair regrowth, then reappeared on its own a month later and is now growing and bleeding — is a pattern I'd want a vet to look at soon rather than treat as a simple skin infection at home. I'm not a vet, just someone who researches dog health closely, so take this as perspective rather than a diagnosis.

Why this pattern stands out

A straightforward infected wound or hot spot usually behaves in one direction: it gets worse, you treat it (cleaning, antibiotics, keeping the dog from licking it), and then it heals and generally stays healed. What you're describing — full resolution with hair regrowth, then a spontaneous recurrence in the same spot a month later that's now larger and bleeding — is a different pattern, and it's one that shows up with skin growths rather than plain infections.

What this could be

A few possibilities that fit this kind of history:

Mast cell tumors are the most common skin tumor in dogs, and one of their well-known quirks is that they can change size — sometimes shrinking or looking like they're resolving — before flaring back up larger, especially with irritation, licking, or handling. They also commonly ulcerate and bleed at the surface as they grow, which lines up with what you're seeing.

A chronic infected cyst or draining tract (sometimes called a furuncle) can also heal over, then rupture and recur in the same spot as it refills, though these usually look more like a single opening rather than the raised, glistening surface in your photo.

A granuloma — an overgrowth of inflamed tissue, sometimes from a lingering infection, foreign material under the skin, or excessive licking — can also come and go and eventually start bleeding if your dog keeps bothering it.

I'd genuinely rather not guess further than that, because the only way to actually tell these apart is with your vet doing a fine needle aspirate (a quick, low-stress test where they pull a few cells with a small needle and look at them under a microscope) or a biopsy if needed.

Why I'd act on this fairly soon

Growth that's enlarging, changing, or bleeding on its own (not just from being bumped) is generally considered one of the signs that should move a lump from "watch it" to "get it checked," and that's exactly what's happening here. It doesn't necessarily mean anything serious — plenty of these turn out to be very treatable, and even mast cell tumors have a good prognosis when caught and removed early. But the recurrence and growth are exactly why waiting isn't the best move.

In the meantime

Keep your dog from licking or chewing it if you can (a cone helps), avoid squeezing it or applying home remedies, and try to get him in this week rather than waiting to see if it resolves again on its own — given it's already come back once and is now bleeding, I wouldn't count on that happening a second time.

I hope it turns out to be something simple, Diana. Let us know what the vet finds.

— Jeff from the dog-health-guide.org team

This response is intended to provide general information and perspective for pet owners and is not a substitute for veterinary diagnosis or care.