Piggies developing bald patches. Two piggies so far. Any ideas of the cause?
I agree with
@Piggies&buns .
Please see a vet because we cannot reliably diagnose just from a picture but you are most likely dealing with a ringworm (tinea) outbreak. Strict hygiene measures and either oral treatment or medicated dips or baths are crucial.
Don't treat before you see a vet (it makes a diagnosis impossible) and don't just cream because that never gets on top of the thousands of invisibly tiny, long-lived, highly contagious species jumping spores that can cause reinfection for up to over 2 years later. You can catch ringworm from your guinea pigs, too. So can any dogs, cats, rabbits etc.
Please read our ringworm guide and follow it. In nearly 20 years on this forum and with our own experiences, we have been able to work out how to stop it most effectively and how find and to cut off all possible transmission routes. If you do it right - it is admittedly a nuisance, but it is a very necessary nuisance - then you can get on top of it in one go.
Invest in one of our recommended disinfectants (ideally F10 concentrate) if you can find it online. Disinfection is your biggest weapon against ringworm to get on top of the spores and prevent ringworm from coming back again and again and again.
Ringworm doesn't kill but it is the most infectious and persistent problem that you can come up against as a pet owner. You underestimate it at your own peril. It is not pleasant when it you catch it yourself, either.
Please let us know what your vet says and what they prescribe. If they want to just use cream, please ask for a medicated shampoo.