My pig has bump on her back

Question
My guinea pig has big bump on her back near her hip.  It feels rubbery. I can't tell if it's red or not because she is black. She scratched it and there is some black thick stuff coming out. What is this and what do I do about it?

Answer
What you see is called a sebaceous cyst. Humans also get them. It's an oil gland that did got plugged up, so the sebaceous material inside fills the gland and begins to swell. The job of the sebaceous glands is to secrete this oily substance into the skin to keep it soft and pliable. If you think of them like a strainer with the holes plugged you get an idea of what's happening.

These glands are not malignant (cancerous) and can get large if not opened and evacuated. It is not painful to your pig.  The stuff inside very thick and is the same color as the skin. If it were a white pig the material inside would also be white. In your case you have a black pig, so the material is black.

If you are comfortable opening in you can use a very small exacto blade such as you get at the hobby shops. It doesn't take much to put a small hole in the lump. Once you have opened it you need to press on it on either side to express the black material inside.  You will be surprised at how much is in there. It may take squeezing it every day for about four days before you stop getting that black goo from it. Once that stops the hole will close over.

It may possibly return as many of them do. But it's not something that is going to threaten her life and I've never seen any of them get infected And I've done these dozens of times over the years.  If you're not comfortable treating it you can certainly ask your vet to do it.  

Please let me know how it works out for you.