Recently, a woman surnamed Wang saw a doctor for eye discomfort and was shocked to learn that lice were the culprit!

The doctor found nits and live lice at the base of her eyelashes.

Based on the lice's appearance and the area of infestation, the doctor concluded that they were likely pubic lice. Fortunately, Wang sought medical attention promptly, preventing significant damage. Her ocular pediculosis was treated effectively.

This news brings up the question—who knew lice still exist?

It also triggers a flood of nostalgic memories for those who battled lice as children.

When I was a kid, lice were rampant.

How rampant? For a while, almost my entire ten-minute recess was spent picking nits, and I mean several of us huddled together picking nits. (Kids weren't squeamish about it back then.) It looked like a bunch of mama monkeys picking nits off their babies.

My deskmate has long hair (whereas I have super short hair), while there are always nits in her hair that can't be removed. It never stops!

When in class, I would accidentally notice many nits crawling around on her head.

Case of Insecticide Toxicity: Pesticide Fumigation of the Scalp

She also tried out lots of methods. Rumor has it that her mother sprayed diluted dichlorvos (a toxic substance that should not be used on the skin) on her head, and used a roach pencil (also toxic and should not be used) and frequently combed her hair with a lice comb. However, the lice on her head could not be eradicated. They were too persistent and kept reappearing.

Thinking back on this experience, I can't help but scratch my head.

Almost everyone had lice in the past. Why are they suddenly nowhere to be seen? Have they become extinct? Lice: Intimate Partners of Humans

Lice, with over 5,000 species, each with its preferred host, mostly infest animals. However, three distinct species target humans: head lice, body lice, and pubic lice.

Head lice reside primarily in hair, body lice hide in clothing seams, and pubic lice infest pubic and sometimes axillary (underarm) and eyebrow hair.

These three lice species differ markedly in appearance and cannot interbreed.

Head and body lice belong to the family Pediculidae, while pubic lice are in the family Pthiridae.

Physically, pubic lice are the largest, with a crab-like shape. Head and body lice are more slender, with head lice being the smallest.

Body lice pose the greatest risk to humans as disease vectors due to their blood-feeding behavior. Historically, louse-borne diseases were widespread.

Despite their reviled status, lice are valuable research subjects for scientists studying human evolution.

Genetic studies reveal a common ancestor for the three human lice species despite their speciation and reproductive isolation.

Why did three distinct species evolve on the human body? Scientists theorize that it's linked to hair loss and clothing adoption.

Human hair loss created geographic barriers, leading to separate head and pubic lice lineages. Later, when humans began wearing clothes, a subset of head lice adapted to this new habitat, giving rise to body lice.

By unraveling the divergence time of these lice, scientists can estimate the approximate timing of hair loss and clothing adoption in humans.

Biologist David Reed's genetic analysis of head and body lice suggests they diverged around 170,000 years ago, indicating that humans were already wearing clothes at that time.

The split between head and pubic lice occurred around 1.2 million years ago.

Thus, humans lost their body hair about 1.2 million years ago but only began wearing clothing about 170,000 years ago, remaining naked for a significant 1 million years in between.

Why Head Lice Are Much Rarer Nowadays

The prevalence of lice in the past was largely due to poor hygiene and a lack of knowledge about it.

In my childhood, people generally washed their hair once a week. It was even more infrequent for my parents' and grandparents' generations. As my grandfather said, they barely had enough to eat, so hair hygiene was not a priority.

Although living conditions improved during my childhood, our personal hygiene and scientific literacy were still lacking.

For example, did I wash my hair once a week because of poor living conditions?

Of course not. At the time, it wasn't customary to wash hair every other day or every day, and we didn't feel dirty.

Moreover, lice are contagious. When children played together, if one child carried lice, the whole group would likely become infested. Once someone had lice, it was challenging to eliminate them completely because their eggs adhere firmly to the hair roots.

Nowadays, our lives are healthier and more hygienic, and we are more scientifically informed, which naturally reduces the likelihood of developing lice.

Additionally, we frequently use scented body washes and shampoos. When doing laundry, we use a lot of detergents and washing powders. For lice, humans are not as "clean" as they used to be, and these conditions make it difficult for lice to survive, accounting for their reduced prevalence.

However, that does not mean lice have been eradicated. Infection Rates and Prevalence

It's estimated that about 14 million people get head lice each year in the United States alone, and children are the most frequently affected. Other countries with high rates of head lice include Denmark, Sweden, and the United Kingdom.

Myth-Busting: Cleanliness and Lice

Contrary to popular belief, head lice aren't necessarily caused by dirty or unhygienic hair.

Scientific Findings: Preference for Clean, Curly Hair

Research has shown that head lice prefer clean, thick, and curly hair. Oily hair, on the other hand, makes it more difficult for lice to cling to. Thus, clean, non-greasy, and naturally curly hair provides an ideal environment for lice to thrive.

Humorous Observation:

Some people have joked that "the reason we have fewer lice these days is because we have less hair!"