Hi!
We generally recommend to have any new piggies that don't come from a good standard rescue with mandatory quarantine and vet care checked through by a vet. In the UK, the first vet check is sometimes discounted when you register your piggies.
It is very difficult to see from your picture what exactly is going on. It would be good to make sure with a hands-on examination that it is not a potential fungal infection. We have heard so many explanations from for sale breeders for the presence of bald patches caused by their failure to treat their breeding stock properly against fungal skin infections and parasites (that would cost money, after all), that we have become rather wary.
What to check and look out for in new guinea pigs (vet checks, sexing, parasites&illness)
Here is what the mechanical abrasure of hairs on the inside of the front paws looks like in 5-6 months piggy. it is a gradual process of hair loss as it is caused by the piggies wiping spit over their coat several times a day in order to clean themselves ('piggy washes'). The older a guinea pig, the less hair in that area. Babies are generally born fully haired in that area.
Your scab does not look like this as far as I can make out; in fact it looks rather fungally to me, but only a hands-on vet examination can decide that. Please do not treat on spec with any cheap products that can only temporarily suppress but not cure any problem and in the end cost you more than if you had seen a vet straight away with a minor case.
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The green link above is part of our new owners guide collection, which specifically addresses all the areas we get the most questions and concerns about from new owners and provides practical information to help to as smooth a start as possible as well as to minimise any preventable problems in the longer term. It includes guides on settling in, safe handling and making friends with; understanding behaviour; diet, housing, care and safe/unsafe enrichment; learning what is normal and what not and how to check for it; early signs of illness and how
You can access the very useful collection by clicking on this link here:
Getting Started - New Owners' Most Helpful Guides