Kitty boogers-normal?

I have always been in the habit of keeping my cats eyes, ears and nose clean-so that they get used to the vet touching them when they have to go for checkups and such- plus its a good way to know if my cats are healthy. Anyways- My kitten seems to have lots of dark "boogers" could it be from dust in the house? the litter? The other cats dont have them...? Should I be conserned of just keep my eyes open.. this is not something new with my kitten.