Haze Checker · Singapore PM2.5
The haze, in cigarettes
How much time in today's haze adds to an adult's long-term health risk, counted in cigarettes, and how much each kind of mask cuts it. A rough comparison from published studies, not a measurement of your body.
By Dr Erah Anwar, PhD, skin scientist
Evidence from PubMed · model v1
PM2.5 right now (1-hour reading)
Loading NEA readings…
NEA guide, next hour: Continue with normal activities.
From NEA's 1-hour guide. NEA counts children as vulnerable, alongside older people, pregnant women and people with chronic heart or lung disease. MOH calls following this guide the key precaution for children.
Up to 8 hours. NEA's 1-hour reading is for the next hour and changes through the day.
Mask
Exercising outside?
Breathing (adult)
You breathe in more air when you move. This option assumes risk rises with the air you breathe in; the main number uses an average day.
For an adult
0.2cigarettes
1 hour outside at 50 µg/m³ without a mask adds about as much to an adult's long-term health risk as smoking 0.2 cigarettes.
Range across our methods: 0.1 to 0.3. Not a full uncertainty range.
At this level, every 5 hours outside adds about one cigarette's worth of long-term risk for an adult
This counts only the hours you set, as a share of a normal day in this air. It is an average for adults of all ages and a way to add up exposure, not a prediction for you. In the studies behind it, the extra risk followed the air of roughly the past one to two years and fell when the air improved.
MOH says healthy people generally have no major health issues from a few days of haze, other than irritated eyes, nose and throat. HealthHub adds that there is little robust data on the longer-term effects of short haze episodes like Singapore's, so read this number as a way to compare air, not a forecast. Children, older people, pregnant women and anyone with a heart or lung condition should follow MOH's stricter advice. How it's worked out
What each mask does
At 50 µg/m³ for 1 hour, worn the usual way. Numbers are cigarettes for an adult.
No mask
breathes it all in
0.2
Cloth
for comparison
30% less
0.1
Surgical
medical, ear-loop
55% less
0.09
KF94
Korean standard
55% less
0.09
KN95
Chinese standard
60% less
0.08
N95
US standard
90% less
0.02
The bar is our central estimate; the thin line is the spread across mask studies. The % is how much less PM2.5 an adult breathes in while the mask is on, from studies that measured what wearers actually breathe in. The central values are our judgement across those studies (cloth is an estimate), not the 94 or 95 printed on the box.
Why KF94 and KN95 score below N95 here
Their filters are as good as an N95's, which is why MOH treats them as equivalent. The difference is the ear loops: on real faces, air leaks round the edges, and worn straight from the pack they do little better than a surgical mask. With an ear-loop clip or a strap behind the head, they cut about 75% to 80%. A surgical mask leaks even with a clip, and MOH says surgical masks are not effective against fine particles.
- Count only the time the mask is on and over your nose. Pulling it down, or a beard, cancels most of the protection.
- If you do need a mask, choose one certified as N95, KN95, FFP2 or KF94 and make sure it seals. Most people do not need one for short trips (MOH). Some masks sold as pollution masks cut very little in dummy-head tests, and fake KN95s are common.
What MOH advises
- For healthy people, a few days of haze will generally not cause any major health issues, other than irritation of the eyes, nose and throat. It is generally safe to carry on outdoors at reduced intensity or duration, unless the 1-hour reading is in Band 4 or a hazardous PSI is forecast.
- An N95 or equivalent (KN95, FFP2, KF94) is not needed for commuting to school or work, or indoors.
- Band 4 (251 and above): healthy people should minimise all outdoor activity. If you must be outdoors, an N95 or equivalent with a good fit may reduce exposure.
- Band 3 (151 and above): older people, pregnant women and people with chronic heart or lung disease should avoid outdoor activity. If they must be outdoors, they may wear an N95 or equivalent.
- Older people, pregnant women and people with severe heart or lung problems should consult their doctor before using an N95. Women in the 2nd and 3rd trimester should not wear one for long.
- Anyone unwell, especially older people and children, should seek medical advice.
From moh.gov.sg/others/haze, as of 17 Oct 2026. MOH's advice comes first; this site only explains the science.
For parents
The number is for an adult. Children are different.
- For a child, the official step is NEA and MOH's hour-by-hour guide: avoid strenuous outdoor activity when PM2.5 is 56 or above, and avoid all outdoor activity when it is 151 or above. MOH calls following it the key precaution for children.
- There is no fair way to turn a child's haze exposure into cigarettes. The numbers on this page come from adult smokers and adult air-pollution studies.
- Children breathe in more air for their size: about 2 to 3 times an adult's per kilo of body weight at ages 3 to 6, and their lungs are still growing.
- Adult masks fit children badly. In a Dutch lab test, 11 children aged 5 to 11 wore the same FFP2 (the European N95) as adults: the typical child still got about 94% protection, but about a quarter got less than 90%, so on average it cut what they breathed in by about 80%, against about 97% for adults. Most KN95s sold for children in Indonesia and Nepal fitted poorly. A child-sized N95-class mask fitted all 106 children aged 7 to 14 in a Singapore trial, but raised the carbon dioxide they breathed unless its fan was on. MOH says there is no international certification standard for children's masks, and names that mask for children without heart or lung conditions, only where necessary. Ask your doctor before putting a respirator on a young child.
- So for a child the strongest move is staying indoors with windows shut and the air-con on, and a HEPA purifier in the room where they sleep.
Quick table: one hour outside
Cigarettes for an adult, per hour outdoors at an average breathing rate, masks worn the usual way. Multiply by your hours.
| PM2.5 µg/m³ | NEA band | No mask | Surgical | KF94 | KN95 | N95 |
|---|---|---|---|---|---|---|
| 25 | Band 1 (Normal) | 0.10 | 0.05 | 0.05 | 0.04 | 0.01 |
| 55 | Band 1 (Normal) | 0.23 | 0.10 | 0.10 | 0.09 | 0.02 |
| 100 | Band 2 (Elevated) | 0.42 | 0.19 | 0.19 | 0.17 | 0.04 |
| 150 | Band 2 (Elevated) | 0.63 | 0.28 | 0.28 | 0.25 | 0.06 |
| 200 | Band 3 (High) | 0.83 | 0.38 | 0.38 | 0.33 | 0.08 |
| 250 | Band 3 (High) | 1.04 | 0.47 | 0.47 | 0.42 | 0.10 |
| 300 | Band 4 (Very High) | 1.25 | 0.56 | 0.56 | 0.50 | 0.12 |
How this is worked out
- One cigarette ≈ 10 µg/m³ of PM2.5 for a whole day, for an adult. We worked this out from PubMed studies using three kinds of evidence (risk per cigarette, deaths per cigarette, years of life lost). Our main methods give 7 to 16, and we show a range of 6 to 17; other reasonable choices go further either way. The clearest route: lifelong smokers who keep smoking lose about 10 years of life, roughly 15 minutes per cigarette, and air that is 10 µg/m³ cleaner adds about 0.61 years of life, almost all of it through adult years.
- One hour counts as one twenty-fourth of a day. The studies behind the number follow people for years, so an hour's figure is an extrapolation: it is what that hour adds to your long-term exposure, not what happens in your body during it. Studies suggest PM2.5's effect follows the past one to two years of exposure and fades when the air clears, while much of smoking's harm builds up over decades. So treat it as a way to add up exposure, averaged over adults of all ages, not a prediction of your own risk.
- Masks are scored on people. A certified filter catches most PM2.5. Air leaking round the edges is what limits protection, so we used studies that measured what wearers actually breathe in.
Why our numbers are higher than other calculators
Most haze calculators use a 2015 rule from Berkeley Earth: 22 µg/m³ for a day is one cigarette. It came from one method, smoking deaths in the US set against air-pollution deaths in China, counted over people of all ages. Redone with newer estimates, which find about twice as many pollution deaths, and counted per adult, the same method gives about 7. Our other methods land near 10, so our numbers are about twice those of calculators that use 22. Berkeley's rule is not a peer-reviewed paper; if you prefer it, divide our number by 2.2.
What this number does not tell you
- It is an average across adults of all ages, not your own risk. Age, heart and lung conditions and how much time you spend outdoors all change it.
- PM2.5 can trigger heart attacks within hours, and asthma flares within days, in people at risk. The cigarette number does not capture that.
- It compares total deaths only, not illness. Smoking adds a large lung cancer risk; PM2.5 harms mostly through heart and lung disease.
- Smoking risk does not rise in a straight line: one cigarette a day carries about a third (women) to a half (men) of the extra heart-disease risk of twenty a day. So "0.5 cigarettes" means half of an average cigarette's share of the harm, not the risk of trying one.
- It compares health risk, not the weight of particles. By weight, a day of haze is far less than a cigarette. But heart risk rises steeply at small doses and levels off at large ones, so the small dose from polluted air carries more heart risk per microgram than one more microgram on top of a smoker's huge daily dose.
- It could be too low. Haze smoke may be more harmful than city air for the same reading: studies of fire smoke find a bigger short-term effect on deaths, roughly 2 to 3 times, though these are different studies so the ratio is rough. An hour actually spent outdoors probably counts more than the average hour in the studies, where people were mostly indoors. And Singapore's yearly average sits on the steep part of the risk curve.
- It could also be too high. We compare with an average cigarette's share of harm; a smoker's first cigarette of the day carries more risk, and measured against it the same air would count as roughly 3 to 6 times fewer cigarettes. We also treat every hour as adding up the same way, and no study has tested that. Counting only the same-day effects seen in daily-death studies would give 3.5 to 12 times fewer cigarettes, but would miss the long-term risk this number is about.
- The risk in these studies follows the air of roughly the past one to two years and falls when the air improves. One hazy week is not a permanent mark.
The routes to the constant
| Relative risk per cigarette vs per µg/m³ (smokers and PM2.5 cohorts) | 9 |
| Deaths per cigarette vs per µg/m³-day, per adult (GEMM exposure curve) | 7 |
| Life lost: about 15 min per cigarette vs Pope 2009, adult years | 9 |
| Life lost: about 15 min per cigarette vs Correia 2013, adult years | 16 |
| Deaths per unit, GBD exposure curve (shown, not counted) | 16 |
| Headline (middle of the counted methods, rounded) | 10 |
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