Hi,,Ok we used to have a cat whom did this all the time,,,the doc told us he could find no reason,,besides that it may have been in our cat,,,a case of nerves..Callie we called her our scaredy cat...she was very shy,,and didn't like change or strangers...He said the usual reason were,,,dry skin,,,you can use tea tree oil on a cats fur and it will help..or fleas,,spray with flea spray or use again the tea tree oil,,(good for many things) or it could be like the others have said,,could be caused by pain of some kind...

Good Luck