It sounds like its Chelitis...

Chelitis is a scabby stitch - it is not advisable to pick this scab off the nose as the skin underneath is tender and picking off the scabby surface will be painful for the guinea pig. The knobbly scabs drop off on their own, although this does not rid the cavy of the infection.

Treatment can be....
Daktarin Oral Gel
Daktarin Antifungal cream
Canesten

I have some pigs and they have never been treated for it and the line of hard skin stays but it does not affect the pig.

Some more information.... Guinea Lynx :: Cheilitis

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