Like many other parents, I’ve paid my dues when it comes to head lice. It was a while ago, back in day care, and there was a dress-up box with hats and crowns and helmets that was probably the smoking gun. We all had to do the whole routine, applying insecticide rinses to our children’s heads and washing sheets and pillow cases in hot water, and becoming somewhat fanatical about not sharing hats.

Meanwhile, my parents, who had grown up in New York tenements, were vaguely horrified that their affluent privileged grandchild was acknowledged to have what they thought of as a mark of disgrace, an infestation that went with poverty and dirt.

And yes, eventually I became convinced that my own head was itching, and bought my own bottle of rinse, though I suspect I was by that point treating phantom lice. Since then, I have checked many heads in the exam room, and I have seen kids with lice, kids with nits, and kids with nothing much going on in the lice department — and I have learned to suppress the phantom lice response; I wear gloves and I wash my hands.

One aspect of the confusion around head lice is that we may think of them as “infectious” because they are spread from person to person — but they do not actually carry infections. They’re just bugs, and technically, we call head lice an infestation rather than an infection, but that doesn’t necessarily make anyone feel any better. (Body lice are different — they can indeed spread infections, most famously typhus).

So when it comes to head lice, the pediatric role in recent years has largely been to reassure, to beg for calm, and to try to get kids back to school as quickly as possible.

The American Academy of Pediatrics put out its latest clinical report on head lice in 2015, a joint project of the group that focuses on school health and the committee on infectious diseases. The report reiterated longtime pediatric positions, emphasizing the importance of careful diagnosis, by trained observers, and arguing first and foremost that children should not miss school because of head lice or nits.

“Misdiagnosis is really common, even with medical personnel,” said Dr. Mary Anne Jackson, the director of infectious disease and professor of pediatrics at Children’s Mercy Hospital in Kansas City, Mo., who works with the A.A.P. committee on infectious diseases.

She said administrators at one school she worked with worried that its football field might be a source of lice, and were concerned with fumigating or otherwise disinfecting it. But unless the players are sharing helmets they are unlikely to transmit head lice.

There are many misunderstandings about head lice, Dr. Jackson said, including the persistent idea that a child with head lice is evidence of an unclean home. (Head lice are, in fact, one of the great equalizers; just look at all the high end “salons” offering to pick to child’s nits for a hefty fee.)

It’s not necessary to treat all the children in a classroom, or all the people who live in the house, though anyone who shares a bed should get treated. We no longer use some of the more toxic insecticidal drugs that used to be employed, like lindane, which was a potential neurotoxin. The over-the-counter preparations that are available now are much safer, but there are concerns about resistance, so many people resort to prescription drugs. One that is commonly prescribed is topical ivermectin, a drug with what Dr. Jackson called “a strong safety portfolio,” but it can be expensive.

And there are many treatments out there that have no evidence to back them up. For example, Dr. Jackson said, there are clinics using heat on children’s hair, which may work under certain conditions, but there is no regulation of how it is being used “to quote unquote inactivate the lice,” she said. “I am skeptical.”

And then there are the “suffocation treatments,” from olive oil to mayonnaise, applied to the hair in hopes of killing off the insects without resorting to chemicals and insecticides. Some of these probably work some of the time but “all will work no matter how you place them if you don’t have lice,” Dr. Jackson said.

So diagnosis is key — someone experienced should look at the child’s head, looking for lice and not just for nits, since all kinds of debris in the hair can be mistaken for nits; everything from dandruff to dirt to drops of hair care products. And someone who knows the resistance patterns in your area should advise you about whether to use the over the counter preparations or the prescription medications.

The head louse life cycle takes about three weeks; the adult female, about the size and color of a sesame seed, lays about 10 eggs a day, and glues each one to a hair near the scalp. Eggs hatch in about nine days, warmed by body heat emanating from the scalp, and the larvae then leave the egg case (which remains glued to the hair, though it’s now empty) and go through several different developmental stages over the next nine to 12 days, before reaching adulthood and starting to lay their own eggs.

That’s why it can be helpful to treat more than once, usually after about nine days, if you are using a product that does not kill the eggs, or if you see live lice after a first treatment. And there are indeed some lice that are resistant to some insecticides, so it’s important to know what is common in your community.

Removing nits with a fine-toothed comb can be done after treating the child’s head, and usually is most effective when the hair is wet, though still not a short or simple process.

From an infectious diseases point of view, Dr. Jackson compared head lice with pinworms, another parasitic infestation parents regard with fear and sometimes with shame, and which may be treated repeatedly without a firm diagnosis that establishes beyond question the presence of these unwanted passengers on the child’s head — or the child’s tail. People worry, kids get treated, sometimes repeatedly, and the treatments cost money and take time. We spend a billion dollars a year on treatments for head lice, according to the American Academy of Pediatrics.

The A.A.P. has fought hard against “no nit” policies in schools, in the interest of reducing the school absence associated with head lice; the C.D.C agrees, and schools are increasingly unlikely to exclude children for nits, but still, in some schools, the policies persist.

“There should never be a case for a child with head lice spending days out of school,” Dr. Jackson said. “Families should be notified, they should be able to access topical medication and they should be able to re-enter the next day.”