My cat has fleas and I've started treating her yesterday. I used a spot on from the supermarket and put it on the back of her neck as advised. Today I have come home and noticed she has a patch of hair missing in that area and scratches underneath. She doesn't seem distressed and she isnt aggravated when i touch the area so in herself she is fine. Is this normal? Will the hair grow back? Is it a reaction to the treatment or has she scratched it so much in aggravation of the fleas that its removed the hair? Thank you!