Template:Rquote The number of cases of human louse infestations (or pediculosis) has increased worldwide since the mid-1960s, reaching hundreds of millions annually.^[1]

Despite improvements in medical treatment and prevention of human diseases during the 20th century, head louse infestation remains stubbornly prevalent. In 1997, 80% of American elementary schools reported at least one outbreak of lice.^[2] Lice infestation during that same period was more prevalent than chicken pox.^[2]

About 6–12 million children between the ages of 3 and 11 are treated annually for head lice in the United States alone.^[3] High levels of louse infestations have also been reported from all over the world including Israel, Denmark, Sweden, U.K., France and Australia.^[4][5]

The number of children per family, the sharing of beds and closets, hair washing habits, local customs and social contacts, healthcare in a particular area (e.g. school) and socioeconomic status were found to be significant factors in head louse infestation. Girls are 2–4 times more frequently infested than boys. Children between 4 and 13 years of age are the most frequently infested group.^[6] In the U.S., African-American children have lower rates of infestation.^[3]

The United Kingdom’s National Health Service and many American health agencies [1][2][3] report that lice “prefer” clean hair because it’s easier to attach eggs and to cling to the strands; however, this is often contested.

Head lice (Pediculus humanus capitis) infestation is most frequent on children aged 3–10 and their families.^[7] Females get head lice twice as often as males,^[7] and infestation in persons of Afro-Caribbean or other black descent is rare because of hair consistency.^[7] But these children may have nits that hatch and the live lice could be transferred by head contact to other children.^[8]