Head louse (Pediculus humanus capitis) parasitize humans for a long time. Genetic analysis suggest that the ancestors of the lice may have originated about 107’000 years ago, with the ancestor of all human lice emerging about 770’000 years ago. The Head louse is an obligate ectoparasite of humans and spends the entire life cycle on the human scalp in contrast to other human parasites, e.g. fleas. Lice are wingless insects and they feed exclusively on blood.
Unlike Body lice, Head lice are not the vectors of any known diseases. Except for rare secondary infections that result from scratching at bites, head lice are harmless, and they have been regarded by some as essentially a cosmetic rather than a medical problem. It has even been suggested that head lice infections might be beneficial in helping to foster a natural immune response against lice which helps humans in defense against the far more dangerous body louse, which is capable of transmission of dangerous diseases.