They only occur on about 20% of all placentalian mammal species, and are unknown from several orders of mammals (Monotremata, Edentata, Pholidota, Chiroptera, Cetacea, Sirenia, and Proboscidea).

[1] They can cause localized skin irritations and are vectors of several blood-borne diseases.

Children appear particularly susceptible to attracting lice, possibly due to their fine hair.

At least three species or subspecies of Anoplura are parasites of humans; the human condition of being infested with sucking lice is called pediculosis.

Pthirus pubis (the human pubic louse) is the cause of the condition known as crabs.