Odd Bald Spot

hello, umm.... My 9 month old kitten, Pitta, has recently developed a rather strange bald spot on her hindquarters, about the size of a poker chip. It's on her back, just a bit before the tail. I've noticed it was thinning for the past few days, but now it's bare. It's very dry and rough in the area of the spot, and the hair is brittle. She's very soft otherwise.
She does have a few fleas, but they've been going away since it's winter now. She also stays strictly indoors and only eays cat food.
Recently, I did bring a stray home. A kitten. I judge him only at about 4 months old, if that. He is sick (Bhroncitus I believe), and I'm going to take him to the vet soon. I keep him in the bathroom though, away from the other pets, simply because of his current illness. Could stress of a male cat be the cause of the hairloss?

thank you for reading

Your cat might still have fleas, the same thing happened to my cat, a few hid in a pile of dirty clothes, then when I went to wash them they must have jumped on me, then my cat. The bald spots were the first sign, along with the itching. A good way to test is put a white sheet or cloth under your cat. When she scratches, look for dark specks on the sheet. If you have them thats called "flea dirt", and thats all the proof you need its fleas. I used advantage on my cat, and it works great, but first I had to see the vet to get the medicine.

I see, thank you!
I have just never seen that before. Didn't think it would have been caused by fleas. Thanks again

Sounds like it could be a hot-spot, which is caused by biting and scratching due to fleas. A vet visit is definitely in order. If it is a hot-spot, the vet will most likely give you Frontline or Revolution to take care of the fleas and an ointment to sooth the hot-spot. Stress could also be the cause, but it seems unlikely because the area of hairloss is so localized. You would notice other symptoms of stress too. Hot-spots are fairly common and routine for vets to deal with.