over grooming

My cat has just started over grooming his left thigh to the point of his hair starting to fade. On a closer look the patch his tiny little white specks that look like dandruff an some slight larger browny yellow flacks/scabs. Is there anything i can purchase over the counter that will help? His never had this problem before and he's 13 yrs old. If that helps
   
kind regards
   
D x

Little more info please, if your cat an inside cat? Is he/she on flea prevention? You could help keep it clean by mixing hydrogen peroxide and water and wipe on spot twice a day making sure to wipe dry the area after. You could also use a descaling shampoo for cats only if you can find it bathing your cat in it twice a week for a few weeks to see if that works. It is hard to treat topically when your cat is going to lick off everything else that you could try. Sorry can't help more. Could of started as an insect bite or fungus or flea dernatitis.