Study shows connection between teacher illness and classroom toxicity

For the first time, a connection between symptoms occurring in teachers and classroom indoor air toxicity has been proven in an extensive scientific study. The new method used in the study helps detect indoor air problems before symptoms appear.

In several prior studies, the focus has been on finding a substance that causes toxicity in classrooms and comparing the findings with the symptoms of those affected. However, no connection between symptoms and toxicity has been found.

“Nearly 200 microbes that cause symptoms have been identified in indoor air. As a rule, however, these microbes do not reproduce in human bodies. Therefore, no microbes underlying illnesses were found in patients,” says Mirja Salkinoja-Salonen, the microbiologist directing the study at the University of Helsinki.

This time, researchers did not limit themselves to looking for impurities in classrooms. Instead, air and surface toxicity was measured by observing reactions in test cells. For this purpose, they used pig sperm, which is used also in food and drug studies to detect harmful substances.

Not all toxic classrooms were included in the study

The researchers were divided into two groups, one to collect samples from classrooms and the other to collect health data from teachers. The material was collected within one month to eliminate disturbing factors, and the data was combined only after the results gained by both groups had been analysed.

All in all, more than 400 teachers from 15 school buildings of various ages in Helsinki participated in the study. In order to confirm a connection between teacher symptoms and classroom toxicity, only those teachers who had been working in their classroom for at least one year were included in the study data.

In the end, 232 classrooms and teachers were selected for participation. On average, study subjects had been working in their classroom for six years.

“Many teachers with toxicity findings were left out because teacher turnover in certain classrooms was quick, in some cases several changes during one school year. In these cases, it would have been impossible to connect teacher symptoms with the classroom in question,” explains Salkinoja-Salonen.

“Illegal and immoral”

The teachers studied had 136 different symptoms and 50 diseases. As the toxicity level of samples increased, teachers experienced more pain, eye and joint symptoms, feelings of illness, as well as cough and neurological symptoms.

Clinically diagnosed asthma and breathing difficulties were reported two to three times more often in schools where more than one-third of the samples were toxic, compared to schools where the share of toxic samples was less than 20 per cent.

To Salkinoja-Salonen, the most important goal has been the development of indicators that are able to detect problems before symptoms appear.

“At the moment, we are using children and school staff as indoor air quality monitors. That is illegal and immoral. Going forward, problem detection should be conducted by toxicity measurements alone.”

Further information

Mirja Salkinoja-Salonen

Professor Emerita

University of Helsinki, Department of Food and Environmental Sciences


Tel: +358 40 573 9049


Material for the article Building-related symptoms are linked to the in vitro toxicity of indoor dust and airborne microbial propagules in schools: A cross-sectional study, published in the respected Environmental Research journal, was collected in 2011.

Based on this data, the research group has published several accounts, including a report on teacher symptoms for the City of Helsinki Education and Real Estate Departments.