It’s a hygienic horror almost as common in the homes of U.S. schoolchildren as it is in third-world countries: head lice.

And you most likely are about to start scratching your head on this one, despite not having lice yourself.

No matter how clean and conscientious your household may be, it’s a disconcerting fact that infestation of the microscopic, itchy critters is more likely to happen than not. It’s usually never a consideration until the scratching starts or a note from school arrives.

Parents may be clueless about the ugly, socially transmitted reality until alerted by their children’s school, and usually only then by a note of anonymous ambiguity. Usually a mass email will say something like, “Your child may have been exposed to head lice by someone in the classroom who is infected.”

Now may be a critical time to look for the critters, as outbreaks tend to happen more often after time off from school, such as winter break, or even after school closures due to weather.

“It’s just a nightmare,” said Nancy Nelson, 53, as she sat outside a coffee shop near her home in Dana Point, California. “It’s just icky to begin with, and then getting rid of it is super hard. It takes weeks, and then you’re always scared it’s going to come back.”

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Nelson, a self-described “neat freak,” recalled the nasty experience she had with her two now-grown daughters when they were in elementary school in the 1990s.

“Both of them got it in first or second grade. Both had long, thick hair,” Nelson said. “Both were kind of emotionally traumatized — really bummed they had lice. And my older girl had it twice!”

It’s not an uncommon tale, and a generation later the problem may be even worse. Researchers at Southern Illinois University Edwardsville recently discovered strains of louse in 25 states that have evolved to resist the over-the-counter topical medications used for decades to combat the critters.

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“What we found was that 104 out of the 109 lice populations we tested had high levels of gene mutations, which have been linked to resistance,” said Kyong Yoon, an assistant professor of biological sciences at SIUE.

He’s also lead author of the study presented last August at the National Meeting of the American Chemical Society, just before the new school year.

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“If you use a chemical over and over, these little creatures will eventually develop resistance,” Yoon said. “We have to think before we use a treatment. The good news is head lice don’t carry disease. They’re a nuisance more than anything else.”

But that nuisance is casting a wider net. The bugs can’t jump from head to head and are only transmitted through direct contact. Sharing headwear is a known transmitter — and now the popular “group selfies” that we take on cellphones are reportedly linked to an increase in cases among teenage and even adult sufferers.

“Just the thought of lice was the grossest thing in the world,” said 31-year old Dawn Castille, a first-grade teacher in a suburb of Houston, Texas.

An elementary school teacher for eight years, Castille had long dodged the annual outbreak. Last spring, it was different. She wondered about her own itchy scalp, visited the school nurse and learned she had contracted head lice herself.

[lz_bulleted_list title=”Signs of Head Lice” source=”http://www.kidshealth.org”]Nits, or tiny yellow or brown dots close to scalp|Adult lice present|Itchy scalp|Small red bumps or sores|Family member diagnosed|Notice from school[/lz_bulleted_list]

“I just couldn’t imagine I had lice,” a perplexed Castille said. “As a teacher, your students get it all the time. I just was never concerned about it.”

In the early stages of her first pregnancy at the time, she was concerned about the toxic chemicals in over-the-counter and prescription remedies. She consulted her doctor and used a regimen of organic topical treatments combined with rigorous nit-picking using a specialty fine-toothed comb.

Effective, if not essential, in ridding the scalp of lice, and more importantly the eggs left behind, the gritty task of combing through the problem is now a booming business.

“To do it right, you need to do it the old-fashioned way. You need to comb the nits out,” said Dina Shields, 54, of Oakland, California.

Her daughter’s experience with head lice a decade ago spawned Shields’ salon business, Nit Pixies, now with two locations in Northern California. Similar businesses have cropped up across the country.

“It’s been a busier than usual season. I’ve had parents say the meds they’ve been buying over the counter aren’t working,” said Shields.

Her service, which costs about $150, includes a topical treatment using a non-toxic all-natural solution of lavender oil and other ingredients designed to kill the live bugs in one 20-minute sitting. The labor-intensive process of combing out all the stubborn larvae follows.

“That’s the problem,” Shields explained. “Nothing is going to kill the eggs. You have to comb those eggs out so they don’t hatch. If you leave anything behind, one or two, then the problem persists. It’s really frustrating.”