Sales of head lice prevention and treatment products have risen in the past week, according to an Irish pharmacy chain.
Careplus Pharmacy says the spike in sales has coincided with the end of the summer holidays.
Lice are tiny insects that are a particular problem in schools, where they climb from person to person and cause itching of the scalp.
Waterford Pharmacist Liz Murray says if parents notice their children with the symptom, they shouldn't panic.
"It happens, it's a daily occurrence. Where I always put people's mind at ease is when there's been somebody in five minutes before," she said.
"It's not anything to do with cleanliness or hygiene. You'll have somebody who'll get them the first day of school and you'll have somebody who'll get them the last day of sixth year in school.
"It's just the luck of the draw."