Monsoon asthma: why June to September is the hardest season for your lungs

What actually changes

Patients often describe the monsoon as a relief — the dust settles, the air smells clean, the heat breaks. For a large number of people with asthma and allergic rhinitis, it is the opposite, and there are four separate reasons.

Humidity suits the house dust mite. Mite populations depend on moisture in the air, and sustained humidity above roughly 60% lets them multiply in mattresses, pillows and sofas. More mites means more allergen in the bedding you sleep on for eight hours a night.

Damp produces mould. Seepage through walls, condensation, bathroom ceilings, clothes dried indoors because they cannot be dried outside, and the water sitting in air-conditioner trays. Mould sensitisation causes the same nasal and chest symptoms as any other aeroallergen.

Respiratory viruses circulate. Viral infection is the single commonest trigger of an asthma attack, in children especially, and the monsoon months bring more of them. A cold that would be trivial in an ordinary chest becomes three weeks of coughing in an asthmatic one.

Ventilation stops. Windows are shut against the rain, and indoor air — with its cooking smoke, incense, mosquito coils and mite allergen — stops being exchanged.

Thunderstorm asthma

This is worth knowing about because it is sudden and frightening. In the right conditions, the updraught before a storm draws pollen grains up, humidity and electrical activity rupture them, and the fragments released are small enough to get past the nose and into the lower airway — where whole pollen grains would not reach. People who normally have only hay fever can get a severe attack within hours.

The practical response is simple: when a storm is building, stay indoors with the windows shut, and if you have a reliever inhaler, have it with you rather than in a drawer.

The fortnight after the rain, which nobody warns you about

In this clinic, the most reliable cluster of flare-ups is not during the heaviest rain. It is in the two weeks after the monsoon withdraws, when wet vegetation, damp walls and soaked ground begin to dry and mould spore release rises sharply. If your symptoms follow an annual pattern that does not match "the rainy season", this may be why.

What to do, in order of what actually works

• Review the preventer before the season, not during it. If the dose was stepped down in the dry months, late May is the time to discuss stepping it back up. Preventers work by reducing inflammation over weeks; starting one during an attack is too late to help that attack.
• Find the damp and fix the source. Wiping visible mould off a wall while the seepage continues achieves nothing. Look behind cupboards, under sinks, at window reveals and at the AC drip tray.
• Ventilate deliberately. Ten to fifteen minutes of cross-ventilation when the rain pauses, and an exhaust fan run during and after every shower and every session of cooking.
• Deal with the bedding. Wash sheets and pillowcases weekly in hot water and dry them fully — clothes and bedding dried indoors in humid air are a significant mould source. Allergen-proof covers on mattress and pillows help if you are mite-sensitised.
• Do not carpet a damp room, and keep soft toys off the bed and washable.
• Keep a peak flow diary through the season. A falling reading warns you days before you feel much, and it turns "I think it's worse" into a number.
• Get the influenza vaccine before the season, if you have asthma or COPD.
• Have a written action plan that says exactly what to do when symptoms start, before you need it at midnight.

One thing that does not help as much as people hope: an air purifier in a room with an open source of damp. It will remove some particulate, but it cannot outrun a wet wall.

Next step

Get your treatment reviewed before the season, not during it

Bring your inhalers, any peak flow records, and a note of how many times you have needed rescue treatment this year.