Our guinea has a movable lump on her back! :0(

Question
We have 2 guineas, both girls and just a little over a year old - my childrens pride and joy!!One of the guineas coconut has developed a lump in her back which is pea sized. It feels soft amd is movable and she is not in any pain, is eating well and it doesnt seem to be affecting her in any way. I wondered if you might be able to give me some advice as to what this may be.
Thanks

Answer
Most likely this is a sebaceous cyst. Humans get them as well. The sebaceous glands are oil glands that excrete the oils in the skin necessary to keep it soft and supple. If they plug up the sebaceous material is stuck in the gland and forms a lump.

They're not harmful or life threatening, but they will grow because the body is still producing these oils, but they can't get out of the gland so they build up. Many of them will ultimately open on their own. The material inside has the consistency of cottage cheese and usually has a very sour smell.

Sometimes they will empty themselves and then grow back again. I've opened many of them over the years and the secret to getting them to heal is to express out the goo every day until it's not longer forming.

It will not hurt the pig in any way just to leave it alone. It could stay the size that it is now, it could grow or it could open. Whatever it does it's not a malignant or cancerous cyst and will not cause either pain or discomfort to the little patient.

The interesting thing I've learned over the many years of cavies is that the substance inside is always the color of the skin under which it has grown. In other words if it's a black pig, the sebaceous material is very dark gray, in white or cream colored pigs the material follow suit.  

In abscesses the pus is always a yellow/green foul smelling fluid that is the consistency of cream. An abscess will also burst open far sooner and will not just stay as a lump. It is filled with bacteria that can be a serious threat to the health of the pig.

In the absence of a bite or wound I seldom see infectious abscesses on the back. That's why I think this is just a harmless sebaceous cyst that is fairly common even in guinea pigs.