Fur missing

My lovely 7 week old kitten pepper is missing fur on her tail and in her arm pit. When I adopted her I asked about it said it has been like this since birth. I am curious if its contagious to other cats,will it spread? All the good stuff

Top pic of armpit this one of tail

@pepperpurr

Welcome to TCS

Have you noticed whether your kitty have been excessively grooming these two areas lately? Or did you noticed that when you brought her home and it became more widespread? Is is dry looking or scabby looking? It could be some skin allergy.
Maybe you can check with the shelter again since they say it's there since birth and whether have they done anything about it.
If you are afraid whether that it's contagious or not, better bring her to get the area checked by the vet.