Hi - it is worth keeping an eye on the patch to make sure she doesnt scratch and get it infected. Our ginger girl ( they have very sensitive skin with that colouring) had a very similiar size bald patch, you could see the tiny ginger hairs growing back. It didnt bother her at all - - Keep a watch out for mites which will need treatment, but if she is not scratching it sounds like one of those guinea things which they have now and again. I know you cant use human moisturiser on their skin, but the vet may be able to recommend something to work into the patch to stop it getting very dry. Personally I would do nothing unless there are visible signs of it causing distress or irritation.
Very clean, not flakey, no mites, just a 50p size patch of pink bald skin?! It is in the place a back leg would scratch but the skin is undamaged and i've not seen any scratching...guinea alopecia?? Any ideas what it is/whether I need to worry. Otherwise piggy is completely normal and healthy.