guinea pig mouth

Question
kale, collard, corn, grass, sasta daisy leaves, dandilions, oranges, carrots, swiss chard, grass, sunflower seeds and vegetable scraps
-------------------------------------------
The text above is a follow-up to ...

-----Question-----
my guinea pig has blackish gunk on the sides of his mouth. it does not pain him, and he lets me pull it off. he has had it before, and after a while, it just falls off. im curious to know what is wrong.
-----Answer-----
Hi

To be honest, I havent heard of this condition before. Can you tell me a bit about what you feed your piggy.

andy

Answer
Hi again

So the diet you give him is well-balanced and good. I have absolutely no idea about this problem as it is something I have never come across in all my time doing this piggy stuff and owning piggies.

I would consult an experienced vet for an answer or search www.guinealynx.info which has lots of medical stuff on it although I couldnt find anything about this condition.

Andy