Swollen red half circle around nipple

My male cat has a tiny area, about the size of a quarter around his nipple where he is losing hair. He is less than 2 years old and the nipple is a little swollen and around the nipple there is a red half circle, like a crescent moon.

Can anyone please help?? I'm wondering what it is and if there is any home remedies. I can give more details if someone can help.

THANK YOU!!!

Sounds like it's irritated for some reason. Is it just the one nipple? Does he over-groom himself on his tummy?

Yes it's just one of his lower nipples. At first it was only a little red but now the red half circle around the nipple seems darker and bigger. He's very shy and scared so I'm not sure if he's been over cleaning it.

He has an appointment with the vet tomorrow, I was just waiting to see if it went down and hoping it was just a bite. I've been looking up ringworm symptoms because I was scared it was that, but it doesn't look like a ringworm circle.

Let us know what it turns out to be!