Hi, she has another guinea pig with her and the other one is showing no signs of having the same problem. Is there any chance it is just dry skin that got infected?
Hi
Sadly not. 'Dry skin' is simply an excuse for not treating properly or explaining away a skin problem to unsuspecting customers - it is especially common in sub-standard for-sale breeders. Any bare patch that is not symmetric on the other side of the body is suspect and should be seen by a vet.
Here is more information on your recourse if you have bought online or from a breeder:
Rescues (Adoption and Dating), Shops, Breeders or Online? - What to consider when getting guinea pigs
Please see a vet. Untreated mange mites can kill and untreated/undertreated ringworm can become a major headache. The companion will come down with it as well as he is likely also already infected. The sooner you can step in with correct good quality treatment, the less of a battle you'll have on your hands. It is really worth the extra money rather than risking a long battle and then having to finally see a vet with an advanced case; not to mention the unnecessary suffering of your piggies.
You are more likely dealing with ringworm but please accept that we cannot replace a vet and diagnose just from a picture. What we can do is tell you when you need to see a vet and help you during vet treatment and recovery with practical advice and moral support. If you have children, please be aware that they can get ringworm more severely than adults and may need to see a gp for an antibiotic.
PLEASE read our links and follow the advice in the ringworm guide re, disinfection and hygiene measures. We have had 15 years and countless cases of ringworm to work out which treatments are effective and which not, and also find all the possible ways of how it can be transmitted and how to counter them appropriately.
When done properly, your treatment in combination with our very precise hygiene measure will mean that you are rid of it in ca. 2 weeks once and for all; especially if you can break the cycle to prevent the companion and yourself from coming down with it by stepping in before it becomes acute. Any visible patch has unfortunately run its due course and will get worse before it is getting better. The last chapter of the ringworm guide will show you in pictures how an outbreak typically runs.
For more practical new owners care tips and helpful information, we have a little collection that can be accessed via this link here to help you avoid the usual pitfalls as much as possible and help you to a good start for the long term:
Getting Started - Essential Information for New Owners