Ah, a great question! Simply put, yes, you can have nits (head lice eggs) and no present and/or visible lice. There are a few reasons to explain this seemingly strange occurrence:
#1 - Houdini Lice
Head lice are crafty critters who are excellent at hide and seek. In fact, if hide and seek were an Olympic sport, they would undoubtedly gold medal! If you spot nits, but do not see any lice, it is possible that they are hiding and scurrying from the light as you search the hair and scalp; they can move quite quickly! Focus your search to their preferred hideouts, behind the ears and at the nape of the neck.
#2 - Fell Overboard/Abandoned Ship
Another possibility to explain the presence of nits and no lice is that they could have simply become dislodged from the hair. This is why a thorough cleaning of the home is recommended after a confirmed infestation. On the other hand, it is possible that they could have become enticed by another tasty noggin and abandoned ship for greener pastures.
#3 - Nits are dead
Often, after head lice infestation, it is difficult to remove every nit from the hair, and it is quite common for some to be left behind. If you recently experienced a head lice infestation and upon a post-treatment head check, you find nits but no lice, it is possible that these nits are leftover from that infestation and are no longer viable. Nits are so small that it is impossible to determine if they are dead or alive with the naked eye; however, if the egg is more than ¼” down the hair shaft from the scalp, it is safe to assume that nit has hatched or, is no longer living.
What do head lice & eggs (nits) look like?
How to check for head lice
CDC statement on No-Nit Policies