Head lice, (scientific name Pediculus humanus capitis) are extremely contagious—but essentially harmless—insect parasites. Unlike their cousin, body lice (Pediculus humanus humanus), head lice don’t carry diseases. The microscopic insects live in your hair, close to your scalp.
Head lice must feed off another living body in order to survive. Their source of food is human blood, which they get from your scalp. Head lice can’t fly, aren’t airborne, and can’t swim or live in water apart from their host. In fact, they cling to hair strands for dear life when you bathe.
But where do they come from in the first place?
Human head lice are categorized into clades based on their genetic makeup. A clade is a group of organisms that are not genetically identical to one another, but share a common ancestor.
The clades of human head lice, named A, B, and C, have different geographic distribution and varying genetic characteristics. According to the Journal of Parasitology, Clade B head lice originated in North America, but migrated to farther reaches of the world, including Australia and Europe.
The species of head lice Pediculus humanus that affects modern-day humans comes from two different lineages of parasites. Research published in PLOS Biology suggests that one of the types of lice, a “worldwide” species, existed first.
Approximately a million years ago, a newer clade diverged from the worldwide species and was confined to the “New World,” or North America. The divergence of the two species mirrors the evolution of the human species from Homo erectus to Homo sapiens at roughly the same time period.
Head lice is thought to have diverged from body lice, a similar yet distinct species, a little more than 100,000 years ago, according to German researchers at the Max Planck Institute for Evolutionary Anthropology. The discovery of genetic differences between head and body lice supports theories that this time period is when people began wearing clothing. While head lice remained on the scalp, body lice mutated into a parasite with claws that can grab on to the smoother fibers of clothing rather than needle-thin hair shafts.
Head lice are transmitted from one host to another through close personal contact. For the most part, this means that a non-infested person would have to be in head-to-head contact with an infested person. Sharing combs, brushes, towels, hats and other personal items can hasten the spread of head lice.
The louse’s way of travel is crawling. In rare cases, head lice can crawl onto a person’s clothing and on to another person’s hair and scalp, but this must happen quickly. Lice can’t live more than a day or so without nourishment.
Having a case of lice can be embarrassing. A common misconception about head lice is that it is a sign of sub-par personal hygiene. Some even believe that it affects only people of lower economic status. These ideas can’t be farther from the truth.
People of all genders, ages, and social class can catch head lice. However, African-Americans are generally less apt to get lice than their Caucasian, Hispanic or Asian counterparts, according to the National Pediculosis Association. This may be due to the difference in hair texture.
Although head lice can be annoying, proper treatment can eradicate the infestation fairly quickly and painlessly. In existence for basically as long as humans have been around, head lice aren’t likely to become extinct any time soon. However, you can prevent your family from becoming infested.
Don’t share personal items such as hats, scarves, hair accessories, and combs with people—especially those who have head lice. Give each family member their own bedding, towels, and hairbrushes to prevent the spread of head lice.