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Guinea Pigs/a lil small 'lump'


Hi Pat,

one of our 2 guinea pigs, about 1.5 yrs old or bit older recently has had a small little lump growing on her right 'thigh'. it started to be a size of a small sweet pea, it seems to be getting bigger now. I am about to make appointments with a vet, but I also want to have your inputs first, since you have helped us with guinea pigs before and I value your help! thanks!

I just want to have an idea before i spend a lot of money I really don't have to spend for vet bills. thanks.

our guinea pigs have healthy diets of hay and fresh veggies. they have clean water and enough space to house them..

Thanks so much,

sebaceous cyst on dog
sebaceous cyst on dog  

sebaceous cyst
sebaceous cyst  
I believe what you are seeing is a common issue with guinea pigs and is called a sebaceous cyst. Humans get the same thing. Sebaceous glands produce a sticky/oily substance called sebum, with the consistency of cottage cheese.  It is comprised of dead cells and fat.Their job is to excrete this substance into the skin and hair to keep it lubricated and waterproof.

For unknown reasons these glands periodically plug up and cannot excrete the sebum. The result is a build up within the gland that begins to turn into a lump. They're soft to touch and if you feel it with your fingers it will feel loose and moveable.

They are benign and harmless. In many cases they will build up until they rupture. The sebum inside has a sour foul smell that permeates the air. In the clinical setting we remove the entire gland rather than just open it up and squeeze out the excess. If it's not removed it will often plug up again.

These cysts are harmless and are nothing more than cosmetic. They do not cause the animal any pain or discomfort and I've found that they are typically located on the top of the back and thigh areas.

Sometimes the pig will scratch or bite at it and it will break open. If that happens you can press on the lump and much of the sebum will come out. I personally wouldn't go to the vet to have this done only because it's not a malignancy and is simply a cosmetic issue. My recommendation would be to leave it alone and let it take care of itself. It is not an infection or abscess and therefore will not cause any health issues with the pig.

I agree with you Jill, you will spend a great deal of money at the vet and if you feel insecure about leaving it alone then by all means get a vet opinion. This is not in any way related to dietary or environmental issues. They just happen. Humans will have their removed only because they may come up where they are visible and want them removed for that reason. In humans they seem to be most frequently located around the upper back, back of neck and behind the ears where we have the most oily part of our skin. They do occur in other places but not as commonly.

I hope this helps you make a decision. Please let me know. Here are a couple of pictures of this type cyst.  

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Pat VanAllen


As is sometimes the case, people in urgent need of information have a higher degree of expectation than those of us as experts are able to give. The experts on this site do their best to give the most accurate and responsible answers possible. We ask that you remember that it is not our intention nor place to criticize the professional advice given by your veterinarian, nor is it appropriate for us to comment on the correctness of a diagnosis made by a licensed physician. Our knowledge is experience based. Although many years of breeding and showing cavies gives me a wealth of experience it cannot change the fact that we as experts are not veterinarians and therefore may occasionally have to reject questions that appear to be asking us to criticize advice given by the licensed professional. Having raised and exhibited cavies for many years I have extensive experience in cavy care and husbandry. I currently have an active breeding program for pedigreed show animals but do not encourage backyard breeding for inexperienced owners. Although I don't encourage breeding for fun I'm always happy to answer any questions from an owner who is in sincere need of help. Pet owners wanting to breed should understand that even experienced breeders have litter losses. The mortality rate is high in cavies. The chance for losing both sow and pups is always present, even with experience. Although this is a site for experts to assist owners, there is no expert in any field who has all the answers. The wisest thing a good expert can know is their limitations. Not having an answer does not diminish one's ability or knowledge. It simply shows that we recognize our limitations and operate within them.


Raised and shown cavies for many years, having aquired my first cavies in the early 1970's as pets. My caviary currently handles 65 + animals in two different breeds and several varieties. Having been in the health care industry as a licensed nurse for 35 years I have hands on experience with care and needs in both humans and cavies. Member of American Rabbit Breeders Association and American Cavy Breeders Association.

Awarded Lifetime Membership in of one of the oldest cavy clubs in the United States, on whose Board I served as Sec/Treas for six years and currently serving as President. Also editor/publisher of the club's quarterly newsletter. We are strong supporters of our youth exhibitors, most of whom are 4H members who are working on cavy projects. Through these projects they become good responsible citizens. We deal with all aspects of showing, breeding, caring for and sharing experiences in the fancy. The cavy fancy is not a new one but in some areas is still relatively unknown. Our goal is to inspire interest in high quality, responsible breeding to improve the species, not just the reproduction of guinea pigs. Our job is to educate owners to help them make the right decisions and choices in the care of their cavies.

Graduate in nursing. Certified in emergency medicine.

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