Pug Losing Hair Neck

why does my dog lose hair around its neck where its collar is?
He is losing his hair around his neck and it looks a little red. He was wearing a normal collar and a flea and tick collar. I have removed both of them now. He is a chichua/pug.
It might be on too tight or he might be allergic to the flea/tick collar. You might want to try a liquid medicine instead. Make sure you can comfortably fit two of your fingers (side by side) under his collar. If you can’t or it feels snug, make it a little bigger for him.
