Air quality in Vietnamese cities and what it does to your breathing

Visitors who have never thought about air before arrive in Hanoi in January, wake on the third day with a cough and a tight chest, and assume they caught something. They did not. Often they did not. The particulate load in northern cities during the cool months is high enough to produce symptoms in healthy people, and more than that in anyone whose lungs already work harder than average.

This page is about which months and which cities are difficult, what to do if you have asthma or chronic lung disease, and which protective measures are worth the effort. It describes general patterns. It is not an assessment of your own lungs. A breathing problem that is getting worse needs a person, not a page.

A breathing emergency does not wait

Call 115 or go to the nearest hospital emergency department if any of the following is happening. With breathing, deterioration can be quick and the margin for watching is small:

• A reliever inhaler that is no longer helping, or that is needed again within a couple of hours
• Too breathless to finish a sentence, to walk across a room, or to eat
• Lips, tongue or fingertips turning blue, grey or dusky
• Sitting upright and leaning forward to breathe, with the neck and shoulder muscles pulling
• Confusion, agitation or drowsiness in someone who is breathless
• A silent chest — wheeze that has stopped because too little air is moving, which is more serious rather than less
• Chest pain with breathlessness, or coughing up blood
• In a child: skin drawing in between and under the ribs, grunting, or flaring nostrils

Follow the written action plan you came with, if you have one. Call for help while you do it, not afterwards. An inhaler used early on the way to hospital is better than a correct decision made late.

What is actually in the air

One measurement matters for health. Fine particulate matter, written as PM2.5 — particles small enough to travel past the nose and throat and into the gas-exchange parts of the lung. The WHO guideline level for annual exposure is low, and urban Vietnam sits well above it, with Hanoi considerably further above it than the coastal cities.

The sources are a mixture that shifts through the year. Motorbike and truck exhaust at street level is constant, and it is what you breathe while riding. Coal-fired industry adds a regional background. Construction dust is everywhere a city is being rebuilt. Straw burning after the harvest spikes sharply in the Red River delta. And temple incense is a concentrated local source that catches people by surprise.

Ozone behaves differently. It builds on hot, still, sunny afternoons, which is why the southern dry season has a late-day problem even when particulate levels read well.

North, centre and south are not the same problem

Hanoi and the northern cities have a cool-season problem, roughly October through March. Cold air sits under a warmer layer above it. The lid closes, and everything emitted stays near the ground — the same inversion mechanism that produced smog in European cities decades ago. Mornings are worst, and the haze often does not lift. The difference between a good day and a bad one is mostly wind.

The central coast, including Da Nang, generally reads lower. A sea breeze most afternoons and fewer large industrial sources nearby do most of that work. The harder periods are still, humid days before a storm, and the burning season in the surrounding hills.

Ho Chi Minh City and the south have a flatter pattern. The dry season from roughly December to April reads higher than the wet months, when rain scrubs the air daily. For anyone choosing where to spend a long stay, that regional difference is a bigger lever than anything you can wear.

Asthma on a trip

• Bring enough reliever and preventer inhalers for the whole trip plus a margin, and keep a reliever on your person rather than in a hotel room
• Carry your written action plan, in English. An unfamiliar clinician can act on a plan much faster than on a description
• Keep taking the preventer inhaler every day even when you feel well on holiday. Stopping it is the commonest reason a trip goes wrong in week two
• A spacer earns its luggage space. Technique falls apart when someone is frightened and breathless
• Note what sets you off here. Incense in temples, cooking smoke, air-conditioning dust, and the two minutes behind a bus are the usual culprits
• Ride inside a vehicle rather than on a motorbike on a bad air day if you have the choice. Street level is where the exhaust is
• If you are using the reliever more often than usual for several days running, that is the moment to be assessed, not after it becomes an attack

COPD and the humidity question

Chronic obstructive pulmonary disease responds to this climate in a way asthma does not always share. Heavy, humid air is harder work to move. Many people with COPD describe a weight on the chest on wet days that has nothing to do with pollution levels. Air conditioning helps that, and then dries the airways enough to thicken secretions overnight, which is its own problem.

The compromise most long-stay residents reach is air conditioning set modestly rather than coldly, a humidifier in the bedroom, and drinking more than feels necessary so secretions stay loose. Keep rescue medication accessible and vaccinations current before you fly — a chest infection on top of COPD abroad is the scenario that ends trips.

Masks: what filters and what does not

The surgical mask sold on every street corner is designed to catch droplets leaving a mouth. It does very little about fine particulates. The particles are smaller than the filter, and the air takes the easy route around the edges.

What works against PM2.5 is a respirator — labelled N95, KN95 or FFP2. The critical variable is the seal, not the rating. One that gapes at the cheeks is doing the job of a surgical mask, and facial hair defeats it entirely.

Two honest limitations. A respirator is uncomfortable in this heat, and one pulled below the nose protects nobody. And none of them touch gases, including ozone.

Indoor air is the part you can change

• A portable HEPA purifier in the bedroom is the measure with the clearest effect, because it treats the eight hours you cannot leave
• Size it to the room rather than buying the largest. An undersized unit running flat out all night achieves little
• Keep windows shut on bad mornings in the north, which is counterintuitive if you are used to airing a room out
• Switch the air conditioner to recirculate rather than drawing in outside air, and clean or replace its filter — hotel units are often filthy
• Keep incense, mosquito coils and smoky cooking out of a room where someone with lung disease sleeps
• Choose accommodation off the main arterial roads. A room on a quiet lane a block back is measurably different from one above six lanes of traffic

Children, older travellers and pregnancy

Children breathe faster relative to their size, so they take in proportionally more of whatever is in the air. Their airways are still developing. A toddler in a pram also sits at exhaust height, which argues for a carrier on a busy street.

Older travellers and anyone with heart disease matter here for a reason people do not expect: fine particulates provoke cardiovascular events, not only respiratory ones. A bad air day is a reason to do less, and chest pain on a hazy day is not something to attribute to the air.

In pregnancy, raise any new breathlessness rather than filing it under being pregnant — it has other causes that need excluding first.

Checking before you go out

Several apps and websites publish a live air quality index for Vietnamese cities, drawing on both government monitors and a dense network of low-cost sensors. The index numbers are useful for comparing one morning with the next, rather than as a precise measurement. The sensor nearest you may be on a rooftop, in different air from the street.

Use it the way a surfer uses a swell forecast: to decide the shape of the day. On a bad northern morning, swap the walking tour for a museum, move exercise indoors, and travel by car rather than on two wheels.

What a visit can sort out

• Working out whether this is pollution, infection, allergy or asthma slipping out of control — four things producing one cough
• Listening to the chest and measuring oxygen saturation, which separates a nuisance from a problem
• Checking inhaler technique, which is wrong more often than it is right and costs nothing to fix
• Reviewing whether the preventer medication is actually being taken as intended on holiday
• Prescribing where it is clinically appropriate, and saying plainly when the answer is a hospital with imaging instead
• A written report and an itemised invoice for an insurer, and a referral letter in English if a specialist is the next step

The short version

The north is hardest from late autumn to early spring, the central coast reads lower, and the south follows the dry season. Keep taking the preventer inhaler, keep a reliever in your pocket, and clean the air in the room you sleep in. A reliever that stops working, or breathlessness that interrupts a sentence, means 115 or the nearest hospital straight away.