The haze is back. On the morning of 9 October 2026, the 24-hour PSI in central Singapore reached 177 — the highest reading of this year's haze season — and all five regions sat in the Unhealthy range. The smoke is coming from fires in Sumatra and Kalimantan, carried in on southerly winds.
If you run outdoors, the question is not whether the haze matters. It is which number to look at, and what to do with it.
Two numbers, two different jobs
NEA publishes two readings, and they answer different questions.
1-hour PM2.5 — "Should I go out right now?" This is the closest thing to a live reading. NEA advises using the 1-hour PM2.5 concentration for immediate activities.
| 1-hr PM2.5 (µg/m³) | Band |
|---|---|
| 0–55 | Normal |
| 56–150 | Elevated |
| 151–250 | High |
| 251 and above | Very High |
24-hour PSI — "Should I plan a long run tomorrow?" This is an average over the past day. NEA advises using the 24-hour PSI forecast for planning next-day outdoor activities.
| 24-hr PSI | Descriptor |
|---|---|
| 0–50 | Good |
| 51–100 | Moderate |
| 101–200 | Unhealthy |
| 201–300 | Very Unhealthy |
| Above 300 | Hazardous |
Check both on haze.gov.sg, nea.gov.sg or the myENV app before you lace up.
What NEA advises
For healthy adults, NEA's advisory is:
- Moderate: normal activities.
- Unhealthy: reduce prolonged or strenuous outdoor physical exertion.
For the elderly, pregnant women and children, NEA advises minimising prolonged or strenuous outdoor exertion in the Unhealthy range, and those with chronic lung or heart disease are advised to avoid it. At Very Unhealthy and above, the advice tightens further — check the full table on haze.gov.sg on the day.
A long run, a tempo session or intervals are exactly the "prolonged or strenuous" exertion the advisory is talking about.
A runner's way to use this
This is how we would read it in practice. It sits under NEA's advisory, not instead of it.
- PSI Good or Moderate, PM2.5 Normal: run as planned.
- PSI Unhealthy, PM2.5 Elevated: keep it short and easy, or move it indoors. Skip the long run and the hard session — those can wait a week.
- PM2.5 High or above, or PSI Very Unhealthy: take it indoors. There is no training benefit worth it.
- Asthma, heart or lung conditions: follow NEA's advice for vulnerable groups and your doctor's, not a running plan.
Readings change through the day. A reading that was fine at 6am may not be at 9am, so check right before you leave, not the night before.
Practical points
Easy effort matters. Harder running means faster, deeper breathing, which means more air in per minute. On a hazy day, an easy run is not just a recovery choice.
Don't run in an N95. Masks that filter well also make breathing harder under effort. If the air is bad enough that you would want one, it is bad enough to move the session indoors.
Keep indoor air indoor. Close windows at home on bad days. Air-conditioned gyms with closed doors are usually the easier place to train.
One missed week costs very little. Fitness does not disappear in a week of easier, shorter or indoor sessions. Pushing through a long run in Unhealthy air does not buy you anything.
What to do instead
Treadmill runs, gym intervals, HYROX-style circuits, pilates and indoor court sports all keep you moving while the air clears. We've put together six indoor swaps for haze days, with how to keep your running fitness ticking over.
Frequently Asked Questions
Is it safe to run when the PSI is over 100?
At 101–200 (Unhealthy), NEA advises healthy people to reduce prolonged or strenuous outdoor exertion. A short, easy run is different from a long run or hard session. Vulnerable groups should follow NEA's stricter advice.
Which reading should I check before a run?
The 1-hour PM2.5 reading for right now, and the 24-hour PSI forecast for planning tomorrow. Both are on haze.gov.sg and the myENV app.
Should I wear a mask to run in the haze?
We would not. A mask that filters well makes breathing harder under effort. If conditions call for a mask, move the session indoors.
Is the morning better during haze?
Not reliably. Haze levels depend on wind and the fires, not the clock. Check the live reading rather than assuming early is cleaner.
How long does the haze season last?
It varies by year with the fires and the winds. Follow NEA's daily haze updates for the current outlook.
Health information in this article is taken from NEA's haze advisories. It is general information, not medical advice. If you have a medical condition, follow your doctor's advice.