Thunderstorm Asthma

Photo One by By Dartmouth Electron Microscope Facility, Dartmouth College - Source and public domain notice at Dartmouth Electron Microscope Facility ([1], [2]), Public Domain,

Pollen from a variety of common plants: sunflower (Helianthus annuus, small spiky sphericals, colorized pink), morning glory (Ipomoea purpurea, big sphericals with hexagonal cavities, colorized mint green), hollyhock (Sildalcea malviflora, big spiky sphericals, colorized yellow), lily (Lilium auratum, bean shaped, colorized dark green), primrose (Oenothera fruticosa, tripod shaped, colorized red) and castor bean (Ricinus communis, small smooth sphericals, colorized light green). The image is magnified some x500, so the bean shaped grain in the bottom left corner is about 50 μm long. (Photo One)

Dear Readers, I was recently intrigued (and a little disquieted) to learn that people with asthma often suffer attacks (known as bronchospasms) following local thunderstorms, to such an extent that hospitals can be overwhelmed. I know that atmospheric conditions such as pollution can exacerbate many conditions, especially those that affect the heart and lungs, but the link with storms was a new one to me. Whilst my mother always maintained that the prelude to a thunderstorm always brought on a migraine, and my dad’s breathing was clearly worse in London than in Dorset, I was curious to see what was causing ‘thunderstorm asthma’.

Firstly, we need to consider pollen. Pollen contains the precursors to the male sperm of a plant, and needs to combine with an ovule (the female part) in order to germinate. The pollen is protected by a double-layered wall, and in the case of wind-pollinated plants ( known as anemophilous, which literally means ‘wind-loving’) the pollen may also contain an air-sac, to make it more buoyant. Grasses, ferns and many trees are wind-pollinated, and the majority of fungi add to the mix by producing spores. These fine, light particles are what makes life so miserable for hay fever sufferers.

However, one factor in thunderstorm asthma seems to be that many of the people who present at the hospitals are not normally asthma sufferers, though they often have hay fever. And there seems to be little doubt that storms are implicated. This study looked at incidents from the UK, Canada, USA and Australia. The Canadian report noted that emergency admissions for asthma made up between 5 and 17% of the total during thunderstorm periods, as opposed to only 2% normally. In Melbourne, the number of admissions for bronchospasms during two thunderstorms in different years were 154 and 277, compared with a non-thunderstorm count of 26 patients. This can lead to a crisis, with not enough nebulizers or steroids available, as happened in some of the UK events. Unfortunately, one episode of thunderstorm asthma can trigger subsequent attacks in people who had never had asthma before – one doctor believes that such an episode can hypersensitise the lungs, making them constrict in conditions such as cold weather.

So what’s going on? Thunderstorms are intensely active events. At the start of a storm, there’s a substantial updraft of air, which drags pollen, spores and other kinds of particulates up into the clouds. After a storm, there’s a subsequent downdraft as air rushes out of the storm area and back to earth. One theory is that the energy and moisture of the storm is enough to break down the pollen granules, resulting in much smaller particles (including ‘paucimicronic starch grains’ which are a particularly potent allergen). Normally, pollen is trapped by the nasal hairs, which mean that you might get a runny nose and eyes, but your breathing is unaffected. These broken-down particles can penetrate deep into the lungs, causing asthma attacks even amongst people who have never suffered from them before.

Scientists also think that such particles might be deposited in rain particles, and are then released after the water evaporates (often the way in a summer storm). A final consideration is that the electrical conditions in a storm might charge the broken-down particles in such a way that they are actually attracted deep into the lungs.

So, what to do? Given the possibility of local medical services being overwhelmed, there was some hope that an early warning system might be possible (such as those in the UK which give pollen levels and UV levels) but the situation is, as ever, more complicated. Not every storm causes thunderstorm asthma, and there is a nuanced dance between the location of the storm, the amount of pollen present, the levels of other kinds of pollution and the presence of fungal spores, which are just being recognised as another potential cause. It seems fairly clear that the spores produced by certain kinds of mould (such as the Cladosporium family) and by some plant pathogens (fungi in the Alternaria family, which include a variety of blights and cankers) can already cause hay fever, and are possibly the ‘smoking gun’ in outbreaks of thunderstorm asthma.

Photo Two by By, Public Domain,

Spores of an Alternaria fungus (Photo Two)

It seems that we need a lot more research on what’s going on with asthma and thunderstorms, especially as, with climate change, we’re likely to be getting a lot more of the latter. At the moment, the main advice for asthma sufferers seems to be ‘stay indoors with the windows closed and make sure you’ve got your inhaler’. Meanwhile, there seems to be more awareness in health services globally that thunderstorms can cause more health problems than the occasional lightning strike. Yet again, we can see how closely intertwined human beings are with the planet as a whole, which is always worth remembering.

Photo Three from

A public health poster on thunderstorm asthma from Australia (Photo Three)


CreditsThunderstorm asthma: an overview of the evidence base and implications for public health advice 

Thunderstorm asthma season is on now. Are we ready for another event if it happens during Covid-19?

Photo One By Dartmouth Electron Microscope Facility, Dartmouth College – Source and public domain notice at Dartmouth Electron Microscope Facility ([1], [2]), Public Domain,

Photo Two By, Public Domain,

Photo Three from

2 thoughts on “Thunderstorm Asthma

  1. Anne

    As usual, you take a complex issue and deliver it in an interesting and easily understandable manner. This is a phenomenon I was unaware of before – mind you, it hasn’t rained here for ever so long. I will now be on the lookout should we be fortunate enough to experience any thunderstorms during the summer. For us it is a glorious feeling that winter is already on the way out 🙂


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