First Guinea Pig - Concerned About Bald Spot
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- And got the T-shirt
I'd treat it as a fungus. See https://www.guinealynx.info/fungus.html
It may also be a result of barbering due to an itch caused, most probably, by fur mites, Chirodiscoides caviae. Fur mites are not very harmful, certainly not as other mites, but they cause skin irritation. Look for tiny white specks attached to hairs, especially on the rear part of the piggie's back.
They can be eliminated by any standard antiparasitic medication, available at any veterinarian as drops or injection.
They can be eliminated by any standard antiparasitic medication, available at any veterinarian as drops or injection.