NIT LAYERS is a term used to describe the layers of LICE that can be found on a person's head. The first layer is the adult LICE, which are the most visible and can be seen with the naked eye. The second layer is the nymphs, which are immature LICE that are smaller than adults and can only be seen under a microscope. The third layer is the eggs, which are laid by the adult LICE and are also too small to be seen without a microscope.