When your head starts to itch, what’s the first thing that comes to mind?

Since grade school, many of us have been groomed to think “head lice,” the dreaded term indicating that your head is infected with thousands of little scalp-eating bugs.

Just thinking about an itchy head kind of makes you scratch at your scalp, doesn’t it? While an itchy head often just means that your scalp is dry, head lice is nothing to scoff at. They can spread quickly, infecting dozens of kids at a time. Take, for instance, one school district in Pennsylvania.

Dauphin County rests about an hour and a half outside of Philadelphia and Baltimore. It’s home to Hershey, the land of chocolate and Hersheypark, and it’s also the home of the Harrisburg School District, where a recent “unprecedented” head lice outbreak took place.

In 2017, a handful schools in Harrisburg saw over 250 children get infected with head lice, forcing the closure of one of the schools for two days.

The Fosse School, which caters to kindergarten through fourth grade, closed for a Thursday and Friday because over 140 students came down with head lice. Not only that, but almost 50 percent of the students didn’t attend school the following Monday (due to lice or other reasons).

Soon after, another school —the Downey School, which has kindergarten through eighth graders—reported about 100 cases of head lice. A third school in the district, also serving younger children, reported having about 20 cases of head lice at around the same time

To help address the massive outbreak of head lice within their schools, the district’s public relations coordinator said they were in communication with various health departments in the city and around the state “to better understand the origin and scope of this unprecedented lice outbreak.” And that is often the best prevention to outbreaks of head lice: education of what it is and how to stop it before it can infect dozens of children.

The goal is to get ahead of the problem and make sure kids don’t have to miss a lot of school. But before we get into how to stop the head lice, let’s first look at exactly what head lice are and how many people are affected by them.

Who Gets Head Lice, By The Numbers

Head lice are one of the most common parasite infestations in the United States, especially among children. The CDC reports that anywhere from 6 million to 12 million children between the ages of 3 and 11 get infected with head lice every year. This age range—those in preschool all the way up until late elementary school or early middle school—is the most common age group affected by lice.

When it comes to gender, studies have shown that girls are more likely to suffer from a head lice infestation than boys, though the reasons for this aren’t explicitly stated. (Some believe that girls have more close head-to-head contact than boys, which is the primary cause of transmission.)

A report by the American Academy of Physicians says that “all socioeconomic groups are affected, and infestations are seen throughout the world.” The group also says that hair length and the frequency of shampooing and brushing doesn’t affect the likelihood that someone is infected by head lice.

Despite this, the CDC says that head lice is far less common among African Americans than any other race in America. They note that the most common forms of lice found in America “may have claws that are better adapted for grasping the shape and width of some types of hair but not others.”

While children are the most common population affected by head lice, it’s not impossible for adults to contract head lice. This is because they may be in close proximity to infected children, specifically if they work in daycares, schools, hospitals, and other locations with large populations of children.

As one woman explained when she discovered “a city of lice” living in her hair after having an itchy scalp for months, she found that one of her kids had head lice eggs in his hair. But he actually didn’t give it to her, because it was the other way around. And she believes that she may have gotten it from other adults, too, pointing to her frequent plane trips and being in close proximity to hundreds of adults at a time.

So just because your child has lice and you’ve gotten it under control, that doesn’t mean that you or another older family member can’t contract it or be the root cause of the head lice itself.

Keep Calm

Head lice aren’t known to carry or transfer any disease, but all the itching and scratching they cause can have derivative effects. Various diseases and viruses can enter your bloodstream from under your fingernails and through open wounds caused by the irritation of head lice. Despite this, the CDC says that head lice “are not considered a health hazard,” but rather they are an extreme annoyance to us all.

The whole process of getting lice out of your head may take a long time, and you may have to do whatever process you choose more than once to make sure that all of the lice are gone. Don’t cheat the process. “Do the physical labor of getting this out,” Dr. Raj Bhardwaj, a family physician, said. “It’s really gross and it takes a lot of time and your kids have to be patient and you have to be patient and you have to do it more than once.”

There is no need to be embarrassed by head lice, and letting someone else know of its presence can help save the next person from getting it.