When his two sons started to cough persistently, he decided to take them to a clinic, where they were diagnosed with pneumonia.

However, Dat said he had the new condo repainted and furniture polished before his family moved in, indicating that his family's health issues could have been caused by the harmful chemical products that can be found in industrial paint and furniture polish.

A World Health Organisation (WHO) study found that oil lamps and gas and coal cookers in residential housing dispersed many air pollutants harmful to human health, such as benzene, formaldehyde, ozone and naphthalene. Noise and cold climate caused people to close their windows, trapping toxic agents indoors and making exposure to them inevitable.

The concentration of harmful air pollutants in Viet Nam was significantly higher than developed countries' safety standards, a study by the National Institute of Labour Protection (NILP) found.

Ngo Quoc Khanh from the NILP said it was high time for Viet Nam to start regulating air pollutant concentration for offices and residential housing in order to protect the health of its citizens.

Random testing at six offices in Ha Noi revealed a concentration of formaldehyde of 0.046 ppm (parts per million), many times higher than the maximum exposure of 0.016 ppm recommended by the American National Institute for Occupational Safety and Health (NIOSH).

This toxic chemical causes irritation to the eyes, nose, throat and respiratory system, with long-term exposure leading to cancers. The WHO lists formaldehyde as an extremely harmful air pollutant to human health.

Formaldehyde can be found in wooden furniture, bed sheets, drapes and carpets, causing the concentration to be higher indoors. Indoor activity was estimated to account for 80 to 90 per cent of all human activity, making indoor air pollution a serious threat, a study by the United States Environmental Protection Agency concluded.