People did not accept lice as a fact of life. A brief history of head lice notes that (http://nuvoforheadlice.com/test/?page_id=101)
c. 64 AD Dioscorides of Anazarbus, who was a Greek physician
in Nero’s army, wrote “De materia medica”, which was the western world
standard pharmaceutical text for the next 1600 years.[Dioscorides, 64
AD] He suggested that an application of a pitch called Cedria (oil of
cedar), derived either from Kedros (Cedrus libani) or from Cedrelate
(Juniperus excelsa), “rubbed on kills lice and nits.” Similarly, he
recommended that a heated rub of the fruit of the Myrica (Tamarix
germanica, Linnaeus) “is good for those with lice and nits.” He noted
that Garlic boiled with Oregano kills lice and bed bugs. He discussed
internal medical uses of the powdered seeds of Stavesacre(*)
(Delphinium Staphisagria), but did not consider the use of the
powdered seeds as a pediculicide.
The writer cautions that these ancient remedies may be poisonous.
He also notes that human lice separated genetically from the lice chimpanzees get some 5.6 million years ago (before the development of modern humans), and recounts the various treatments developed by the U.S. military and made available to the public (.ca 1940s). Head lice have become resistant to some of these treatments.
I do not know how common head lice (the nits are the eggs) are today; various articles on the Internet discuss treatment in the form, generally, of a lotion or shampoo, which often can be purchased over the counter (without prescription) at a pharmacy. Head lice are highly contagious but not, according to these articles, dangerous; but children with head lice may not be allowed to return immediately to school
Monkeys (and chimpanzees) groom one another by "picking nits," but the treatment for humans depends on killing all of them at once.
There's also a expression "nits and gnats." It shows up on Ngram but is usually transcribed as "nits and nats" (which doesn't show up on Ngram), since the g isn't pronounced:
U.S.-Soviet Accord Near, Shultz Says : Only 'Nits and Gnats' Block
Agreement on Missiles, He Asserts (Los Angeles Times, September 14, 1987).
Gnats are small insects that fly in a swarm.