WATERLOO -- It's a nit-picking nuisance every parent dreads. And with school back in session, chances are greater for the creepy-crawly inconvenience.

"When school starts back up we absolutely do see an increase in head lice cases," said Lanette Kane, director of medical services for Peoples Community Health Clinic.

Head lice, formally known as pediculosis, is a common childhood annoyance. An equal opportunity offender, it does not discriminate based on gender, race, ethnicity or socio-economic status. Hair is hair to this pesky little critter.

"People have the idea that if you get it you're not clean, and that's just not true," said LeeAnn Main, a school nurse at West High School and Kittrell and Black Hawk elementary schools.

According to the Iowa Department of Public Health, mature head lice are about the size of a sesame seed. They live in human hair and draw blood from the skin. This often is the cause of the itching. Lice lay eggs (called nits) on the hair shaft. Live nits are found less than a half-inch from the scalp and most often on hair at the nape of the neck and behind the ears.

Lice spreads almost completely through human hair-to-hair contact, and pets do not spread lice. Head lice is more common among elementary students, particularly among little girls who may share combs, hats or hair accessories. Cases are less frequent among high schoolers.

Still, students in the Waterloo schools missed 273 school days in the 2007-08 academic year because of head lice, Main said.

"The school policy used to be that even if there were nits present, then they couldn't be in school," Main said. "Now it's changed that if there are live bugs present then the student has to go home and have it taken care of. We don't send them home if we see only nits."

The head lice policy differs in the Cedar Falls Community School District. If a student is found to have head lice, parents are notified but the child is not sent home.

"If they are uncomfortable with the itching we may send them home," said Sue Gettman, school nurse coordinator for Cedar Falls schools and the nurse at Cedar Falls High School. "But otherwise, we just ask that parents initiate treatment and we recheck the next day to make sure it's been treated. Lice is a nuisance, not a communicable disease, so we balance that with a student's educational needs."

Opinions vary on how to treat head lice. Some say saturating the hair with mayonnaise suffocates the critters. Others say straight hair conditioner will do the trick.

"Most of the time they can use over-the-counter lice treatments. Those are really effective," Gettman said. "But if there's a real persistent case they can get a prescription for a stronger lice shampoo from their physician."

Whatever treatment is chosen, it must be followed by a careful combing out of all lice and nits with a nit comb, a pain-staking and time-consuming process.

"I can tell you I had a student at the high school who had recurrent head lice because there was no follow through on treatment. For three years I checked her every week, and every week she had it," Gettman said.

Head lice are not dangerous and do not spread disease, the nurses say. But left untreated, the continuous scratching caused by lice can result in sores on the head that may lead to infection.