guinea pig mouth sores

Question
Thank you for your response.  I have not been feeding my pig any apples, tomatoes or grapefruit. She does not receive any fruit at all, in fact. The veggies she eats are romaine lettuce, endive, radicchio, the occasional baby carrot and a treat of cilantro from time to time. It seems that my pig must be getting too much acid in her diet. Can any of the foods I listed cause this?
Again, thank you!

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Followup To
Question -
My guinea pig has developed crusty sores on the corners of her mouth. I have researched on the internet and think it has something to do with vitamin C. The problem has gone on for several weeks now. My pig is still eating and drinking like normal and I have been able to make the sores clear up for a little while and they are much smaller BUT I can't get them completely cleared up. Here are the things I have done to help her:
1. I used genetian violet. At first, I was pulling the scabs off and applying the violet. It was complete torture for her (and me, I cried every time!) This helped a little. Now, I apply the violet every other day or so.
2. I have started adding Vita-Sol multivitamin to her water. This seemed to help a lot too, but still not completely cleared up.
3. I bought a new water bottle and clean it daily with warm soapy water. i also give her cage thorough weekly cleanings.
4. I found pellets with the highest possible vitamin C content for her to eat.
She does recieve unlimited hay, pellets and 1 1/2 - 2 C of fresh veggies daily. She is a happy delightful pig and doesn't seem to be in any pain. I want to get her completely cleared up, obviously. We have a new pig and when the quarantine period is up, I am hoping that the mouth sores will be
gone by then. Otherwise, I don't see how I can put them together. I don't want my new girl to develop the same problem. The vet that I use for my pigs moved and I am trying to find an exotic pet but so far the nearest one is 120 miles away! Can you offer any advice?

Answer -
Hi there Massey!  Scurvy, which is a vitamin C deficiancy causes sores on the body.  It also causes hind end paralysis and dry flakey skin.  I do not believe that your guinea pig has this.
Since the sores are around her mouth, I would definately think that something she is ingesting is causing this.
Large quantities of Apples, Tomatoes and Grapefruit can cause mouth sores.  If you are feeding her any of these fruits, I would stop them for a week or two, and slowly introduce them again, always only giving small amounts.  I would not hesitate to put your new guinea pig in with her when the quarantine period is up, as this is not a contagious ailment.  Alot of piggies are prone to these mouth sores...some have them forever, and some only have them when eating alot of the fruits listed above.  
I hope this is helpful!
Hilary

Answer
Hi Massey.  The treats you have listed, in my knowledge would not cause mouth sores.  Another thought has come to me.  How large are the pieces of treats?  I don't know if this ever happened to you, but did you ever slice the sides of your mouth on a potato chip?  This possibly could be the same sort of thing that is happening to your piggie.  I am going to talk with the veterinarian that I work with, on Monday, about this, and see if he has any more information to offer.  Sorry I couldn't be of more help, but I am determined to find an answer for you!  Hang in there and I will get back to you by Monday night.
Thanks so much!
Hilary