With the  air quality slipping into 'most severe level', those suffering from asthma and heart diseases have been advised to take precautions. People are advised to wear face masks and avoid early morning and late evening walks as concentration of pollutants is highest during this period.

Dr Vikas Maurya, head of the department of  Pulmonology and sleep disorder at Fortis Hospital, Shalimar Bagh, said, "Air pollution levels can cause various immediate health problems other than respiratory problems". It can damage cells in the respiratory system, and cause diseases such as bronchitis, emphysema, and perhaps cancer. Extra stress on the lungs and heart leads to herded work to supply the body with oxygen causing faster aging of the lungs," he said. People should ensure that indoor air pollution does not take place and there is a chimney in kitchen and an exhaust system in bathroom. Schools should avoid outdoor assemblies, sports activities and other physical activities in the early morning hours, they said.

Dr Sandeep Nayar, Director of  Department of  Respiratory Medicine at BLK Super Specialty Hospital said that air pollution has emerged as one of the biggest healthcare challenges and it has put India in an emergency like situation.

Nayar advised people to use good quality masks while stepping out, avoid smoking and keep doors and windows closed when the particulate matter residue goes high.

He further said the country ranks among top nations with pollution-related deaths.

"Prolonged exposure to air pollution can lead to reduced lung function, respiratory infections, and aggravated asthma. Air pollution is both cause and trigger for asthma, he said, adding that air pollution causes a burden through a mix of non-communicable and infectious diseases, mainly cardiovascular diseases, and chronic respiratory diseases such as asthma, lung cancer and lower respiratory infections,"

Talking about the effect of pollution on pregnant woman and children, he said it affects both mother and baby adversely.  It prevents fetal development and hazardous chemical elements such as carbon mono-oxide, nitrogen dioxide present in the air affect the development of the unborn child and sometimes increase the risk of a premature baby. It may cause infertility, miscarriage, irritability, and mental imbalance, he added.  According to the Central Pollution Control Board, the air quantity index was recorded at 416 at 11 am.

"Intake of every 22 micrograms per cubic metre of polluted air is equivalent to smoking a cigarette. So, whether the PM2.5 level is 700 or 300 units, the impact is still as bad. People need to take precautions, especially those suffering from asthma, bronchitis or other respiratory illness," said Dr Arvind Kumar, lung surgeon at the Sir Ganga Ram Hospital here.

Doctors at other hospitals also prescribed dos and don'ts with pollution levels continuing to be in the 'severe' category on Wednesday as a blanket of smog wrapped Delhi.

According to ICMR study, About 4 lakh deaths in India in 2017 were due to air pollution, which included 6.7 lakh deaths due to outdoor particulate matter air pollution and 4.8 lakh deaths due to household air pollution. The highest PM2.5 exposure level was in Delhi, followed by the other north Indian states of Uttar Pradesh, Bihar and Haryana.