What breed is he?
does he have a pushed in face?
is there any black on his chin?
Many kittens get that "dirty nose" because they do not clean up well after eating.You can pat him with a warm damp cloth and apply a dab of vaseline. It will not hurt your baby to lick it.
As long as he does not develope www.fabcats.org/acneandstudtail.html he will be fine.
Please let me know if you have any more questions and how your baby is doing.