Key facts

  • The haze is a preventer problem that people treat as a reliever problem. Needing the quick-relief inhaler more often is the signal that the background treatment is being overwhelmed, not the solution to it.
  • The effect builds over weeks. Smoke inflames an airway slowly, so the bad day is usually the end of a bad fortnight rather than the result of one afternoon outdoors.
  • This is a measured phenomenon, not a feeling. Researchers have linked PM2.5 exposure to asthma exacerbation in children in Bangkok and Chiang Mai (Annals of Global Health).
  • Controller inhalers do not work immediately, which is why starting one when the sky turns is already late.
  • COPD is the less forgiving version of the same story. What asthma recovers from, COPD often only partly recovers from.
  • The season is predictable, so the planning can be too. Supply, reviews and indoor air are all easier to arrange in January than in March.
  • Any real change in your treatment is a review, not a decision to make alone. This article is background for that conversation.

In the second week of March you notice you are counting. You shake the reliever, you listen to it, and you try to work out how many doses are left, because you have been reaching for it in the afternoons and again before bed, and it is going down faster than a month should take. From the window, the hills you can normally see are simply not there. The sky is the colour of weak tea.

Nothing has changed about you. What changed is the air, and the way most people respond to it is the reason a manageable few weeks becomes a bad few weeks.

What smoke actually does to an airway

An asthmatic airway is already inflamed, even on a good day when you feel nothing. That is the part that catches people out: the disease is not the wheeze, the disease is the state of the airway lining that makes the wheeze possible.

Fine particulate matter, the fraction small enough to reach deep into the lung, adds to that inflammation. The World Health Organization sets out the health effects of ambient air pollution and identifies fine particles as the pollutant most strongly associated with harm. In an airway that starts inflamed, the effect is not additive so much as compounding: a lining that is already swollen and producing mucus becomes more so, and the muscle around it becomes twitchier about everything else, including cold air conditioning, exercise, dust and smoke from the street.

The important part is the timescale. This is not an allergic reaction that arrives in ten minutes and leaves in an hour. It accumulates. You can spend a week feeling slightly worse than usual without ever having a bad episode, and then have a bad episode on a day that was not especially worse than the six before it. People reconstruct the story backwards and blame that day. The day was not the cause.

The two inhalers, and the one people reach for

Almost everyone with asthma has two kinds of inhaler in the house, and almost everyone thinks of one of them as the real one.

The quick-relief inhaler, usually salbutamol, relaxes the muscle wrapped around the airway. It works within minutes, it feels like it is working, and that is exactly the problem: it does nothing whatsoever about the inflammation underneath. It opens a swollen tube. It does not make the tube less swollen.

The controller, or preventer, does the opposite. Singapore’s HealthHub describes the steroid inhalers plainly, saying that fluticasone “helps to reduce and prevent swelling and inflammation in the lungs” and is used to control symptoms in asthma and COPD. Combination inhalers work the same way with a long-acting opener added; HealthHub’s page on the beclometasone and formoterol combination calls it a preventer or controller and links it directly to reducing the chance of an attack.

Controllers do not announce themselves. You take one and feel nothing, which is why people drift off them in the good months and why the drifting is invisible until the air changes.

So here is the thing worth carrying away from this article. When the haze arrives and you find yourself using the quick-relief inhaler more often than usual, that is not the treatment working. That is the measurement telling you the background treatment is being outrun. Reaching for it more is data. It is the single most useful thing you can bring to a doctor, and the single most commonly ignored.

What you should not do is quietly increase anything yourself. Adjusting a controller is a clinical decision, it depends on which device you have and what else you take, and getting it wrong in either direction has consequences. Bring the observation. Let someone qualified decide what to do with it.

The season you can see coming

Almost nothing else in medicine gives you this much warning. The burning season in northern Thailand and across parts of the region arrives at roughly the same time each year, and that predictability is the one advantage the patient has.

WhenWhat it is forWhat it looks like in practice
Two months aheadThe reviewAsk whether your current controller is right for the months when the air is worst. This is the conversation that changes the season.
Two months aheadThe supplyWork out what you will need and whether it will be here. Running out mid-season is the avoidable disaster.
Through the seasonThe trackingNote how often you reach for the reliever. Frequency is the number that matters, not how bad any single day felt.
Through the seasonThe indoor airThe hours you spend asleep are the hours you have most control over.
Any timeThe escalationKnow in advance what counts as an emergency and where you would go at three in the morning.
After it liftsThe debriefIf the season was worse than last year, that is a finding. Take it to a review rather than filing it under bad luck.

A note on the last row, because it is the one people skip. Symptoms that improve when the air clears feel like a problem that solved itself. Often what it means is that your background control is marginal, and next year the same thing happens again.

The medicines around the edges

Tiotropium and ipratropium work on a different nerve pathway to open the airway, and are used more in COPD than in asthma, though there is overlap. Salmeterol and formoterol are long-acting openers that belong in a combination inhaler alongside a steroid rather than on their own. Budesonide and beclometasone are the other common inhaled steroids. Theophylline is an older tablet still used in some places, with a narrow margin between a useful amount and too much, which is why it needs closer supervision than most.

Montelukast deserves a specific and careful mention. It is a tablet rather than an inhaler, which makes it attractive to people who dislike inhalers, and it does have a place. It also carries a boxed warning from the US Food and Drug Administration about serious mental health side effects, including agitation, depression and suicidal thinking. That warning is not a reason nobody should ever take it. It is a reason it should be a considered choice with someone who knows your history, rather than something added because the air got bad. We take the same line in our article on allergy relief in Hong Kong.

You can see what we list across respiratory health, and browse by condition under asthma and chronic obstructive pulmonary disease.

COPD, where the air is less forgiving

Everything above applies, with one difference that matters.

In asthma, the narrowing is largely reversible. The airway closes and, treated properly, opens again. In COPD, some of the change to the lung is structural and permanent, so a bad exacerbation is not simply a bad few days. Recovery is often incomplete, and people describe never quite getting back to where they were before.

That changes the maths of prevention. For someone with asthma, a rough haze season is miserable and then it passes. For someone with COPD, it can move the baseline. Which is why the planning above is not fussiness, and why the two-months-ahead review is worth more to a COPD patient than to anyone else reading this.

Masks, purifiers, and honest limits

Both help. Neither is treatment.

A well-fitted mask rated for fine particles does reduce what reaches your lungs outdoors, and a loose surgical mask does much less. An air purifier sized for the room, running in the room where you sleep, with the windows shut, meaningfully reduces indoor particle levels over the hours you spend there. Since you spend a third of the season asleep, that is the highest-value place to put one.

What neither does is reduce the inflammation already in your airway. They lower the exposure. The medicine handles the airway. People who buy a purifier and quietly stop their controller have made the trade in exactly the wrong direction.

Also worth reading

For the year-round allergy picture and how nasal symptoms interact with the chest, see allergy relief in Hong Kong. For keeping supply steady across the region, see buying medicine in Thailand and buying generic medicines in Asia.

FAQ

How do I know if my asthma is actually getting worse or if it is just the air?

From the site’s point of view it does not matter much, because the answer is the same: more reliever use means the current plan is not holding. The distinction is worth making at a review, where someone can look at the pattern across seasons rather than weeks.

Should I start a preventer just for the haze season?

That is a clinical decision and a common one, but the timing works against you. Controllers take time to build their effect, so starting when the sky turns means waiting through the worst part for it to help. The useful version of this question is asked in January.

Is it safe to exercise outdoors when the air is bad?

Exercise makes you breathe harder and deeper, which draws more particles further in. Most people move sessions indoors during the worst weeks. If exercise reliably brings on symptoms even in clean air, that is worth raising separately, because it usually points to control rather than to the air.

My child seems more affected than I am. Is that real?

It is consistent with what has been measured. The Bangkok and Chiang Mai research looked specifically at children, who breathe more air relative to their size and whose airways are smaller to begin with.

When does this stop being something to manage at home?

Breathlessness at rest, difficulty speaking in full sentences, a reliever that is not lasting as long as it usually does, or lips and fingertips changing colour are all reasons to seek urgent care rather than wait it out. Know where you would go before you need to know.

Sources

This article is general information, checked on 10 August 2026. It contains no doses and no schedules, and it is not a substitute for advice from a clinician who knows your history.