Thousands of Kiwi teachers are at risk of developing serious voice problems because of high noise levels and poor acoustics in classrooms.
Research surveying almost 3,000 teachers suggests they have higher rates of voice-use issues than people in other jobs.
Two studies, led by University of Auckland speech experts Sylvia Leao and Professor Suzanne Purdy, have revealed more than a third of teachers have suffered problems with their voices at some point.
Almost 24 per cent say they have had problems in the past 12 months, with primary teachers and women aged 51 to 60 years most at risk.
About 28 per cent of teachers have stayed away from work for up to three days because of vocal problems, and a further 10 per cent have taken extended sick leave.
"The time off not only impacts on the quality of children's education but it is a financial burden on the country," said Purdy, head of speech science at Auckland University.
The new research, unveiled by Leao at the recent World Voice Congress in Egypt, also showed only 22 per cent of teachers with vocal problems sought treatment. About 86,000 teachers work in this country.
"People like singers and auctioneers are tuned into the fact that they have to take care of their voices," Purdy explained.
"But most teachers don't give it much thought, even though it is their main communication tool for doing their work. Excessively noisy classrooms and poor acoustics, especially in newer buildings that have thinner walls, are the main reasons for people developing issues and becoming ill.
"Many senior teachers who are extremely good at their jobs are also retiring early because of this."
The problem has caught the Ministry of Education unawares.
A spokeswoman said the ministry had not been advised of voice problems among teachers.
"Any health issues experienced by individual teachers are addressed in the first instance by the employing board of trustees and the teacher concerned," she said.
Dr David Vokes, an ear, nose and throat surgeon at Auckland City Hospital, said teachers seeking treatment for chronic voice conditions far outnumbered those from other professions. He sees "dozens" of teachers every year.
"Simple laryngitis usually settles down after about two weeks but if symptoms are still present after three weeks, people should see a specialist," he said.
"This is a significant occupational health and safety issue."
A class act with a microphone
Elizabeth Baker has been teaching for six years, but she is already experiencing problems with her voice.
The 44-year-old works at Drury School in South Auckland.
In 2011 she was forced to take six weeks off after losing her voice.
"The principal was very understanding but my sick pay ran out after 10 days," she said.
"ACC wouldn't pay out because I couldn't prove my condition was work related.
"So I had no income for several weeks. It was very frustrating and I also had to spend $400 of my own money to attend a speech therapist."
About 20 months later, Baker said her voice was still not back to normal.
She now used a microphone and amplifier system in class.
"When I'm teaching PE, I also use a megaphone and I gargle with garlic and vinegar," she added.