The worsening haze has led to respiratory-related ailments for business undergraduate Wendi Lai and her family, who complained of breathing difficulties and tightness in the chest.
It has been particularly troubling for Ms Lai, as she also has the flu and believes the haze worsened her sore throat, which had been improving.
"I had to see a doctor on Sunday, and he told me I had lung irritation (due to the haze)," the 19-year-old said.
Doctors told My Paper that the worsening haze could pose health problems for certain groups of people.
Dr Pek Wee Yang, head of Khoo Teck Puat Hospital's department of general medicine, said "asthma attacks and chronic obstructive pulmonary disease exacerbation are more frequent" at unhealthy Pollutant Standards Index (PSI) levels.
Associate Professor John Abisheganaden, a senior consultant at Tan Tock Seng Hospital's department of respiratory and critical care medicine, said that in severe cases, the haze can cause breathing difficulties, especially in patients with chronic heart or lung conditions. Said Dr Pek, who specialises in respiratory medicine: "Even healthy people may have some irritation in the eyes and throat."
Yesterday, the PSI nearly tripled to 155 at 10pm, from 56 at 7am.
A reading between 101 and 200 is considered unhealthy, one in the 51-100 range is moderate and a reading below that is good.
The National Environment Agency (NEA) said yesterday that the smoke haze was from fires in Sumatra, Indonesia. NEA said the hazy conditions are expected to persist over the next few days.
The last time air quality here deteriorated to unhealthy levels was in 2010.
Dr Steve Yang, a respiratory-medicine specialist and consultant at Raffles Internal Medicine Centre, said yesterday that more patients - mainly middle-aged adults and seniors - have been seen at clinics due to asthma and breathing-related disorders.
The haze, he said, was a "significant contributing factor" to this increase.
NEA said that when PSI readings go above 100, children, seniors and people with existing heart or respiratory ailments should reduce physical exertion and outdoor activity. The general population should reduce vigorous outdoor activity.
Dr Clarence Yeo, a general practitioner at Killiney Family and Wellness Clinic, advised the public to drink more water and get enough sleep.
Wearing a mask could help healthy people who experience discomfort, said Dr Yeo. Dr Yang added that air ionisers or purifiers may also offer some relief.
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