Thunderstorm Asthma

Thunderstorm Asthma: St Emlyn’s

Estimated reading time: 4 minutes

In the UK this weekend there are warnings out regarding Thunderstorm Asthma. This is a rare but well described phenomena when patients who are previously known to be grass pollen allergic (e.g. hayfever) suffer asthma like symptoms as a result of thunderstorm activity in the area.

It can take patients and physicians by surprise and can have catastrophic consequences.  The most significant episode of thunderstorm asthma on record was in Melbourne in 2016 when A&E asthma-related hospital admissions rose by almost 1000% during a 12 hour storm.  

Why does thunderstorm asthma happen?

It occurs at times of high grass pollen count in the atmosphere and electrical activity as a result of thunderstorms. Normally pollen is too large to enter the lungs but It is thought that then when exposed to moisture as a result of thunderstorm activity, osmotic shock breaks up pollen into hundreds of smaller, extremely allergenic fragments.  It then concentrates these at ground level and these are able to enter more deeply into the respiratory tract, to cause an allergic response and thus produce a picture of bronchospasm and increased secretions similar to asthma. Other inhalant allergens such as the mould Alternaria (June-September) have also been implicated but fortunately birch pollen (March-April) which causes spring hay fever does not seem to trigger thunderstorm asthma.

The condition may occur in grass pollen allergic patients who are also asthmatic OR it may present in patients with grass pollen allergy (hayfever May-July) but who have not previously suffered from asthma.  All 7 Melbourne epidemics occurred in November when rye grass pollination was at its peak.

Has it happened before?

Almost certainly many times (on the basis of the number of thunderstorms during high pollen counts), with many of these described in the literature. There is a nice review from 2020 here detailing the characteristics of a number of events across the world, and with several occuring in the UK. The impact varies but in some cases it can be profound with reports suggesting that increases of respiratory disease more than 10x the expected or even 1000s of cases across a region resulting from certain events.

It appears that Australia has more events than in other areas (or perhaps better recorded) and they have some excellent public health information approaches such as the video below.

What can we do?

As emergency physicians/clinicians then there is not a huge amount we can do in terms of prevention beyond educating our patients (and ourselves) with the advice below.  Fortunately the vast majority of thunderstorms do not provoke thunderstorm asthma, even on days with high pollen counts. 

thunderstorm asthma

From a clinical perspective we can prepare for an increase in respiratory presentations and consider the diagnosis in patients presenting with asthma type symptoms and a history of pollen allergy/atopy following a thunderstorm.

In terms of treatment then it is appropriate to treat as we would an asthmatic patient but with the addition of antihistamine medications.


Sophie Farooque @LondonAllergy

Simon Carley @EMManchester

Further reading

The Melbourne epidemic thunderstorm asthma event 2016: an investigation of environmental triggers, effect on health services, and patient risk factors Lancet Planet Health. 2018 Jun;2(6):e255-e263. doi: 10.1016/S2542-5196(18)30120-

 M. Hew, J. Lee, N.H. Susanto, S. Prasad, P.G. Bardin, S. Barnes, et al. The 2016 Melbourne thunderstorm asthma epidemic: risk factors for severe attacks requiring hospital admission Allergy, 74 (2019), pp. 122-130

Ajay Kevat1. Thunderstorm Asthma: Looking Back and Looking Forward.

D’Amato G, Vitale C, D’Amato M, et al. Thunderstorm-related asthma: what happens and why. Clin Exp Allergy. 2016;46(3):390–396. doi:10.1111/cea.12709

Asthma UK. Thunderstorm asthma.

Campbell S. Evaluating the Risk of Epidemic Thunderstorm Asthma: Lessons from Australia

Thunderstorm asthma

Cite this article as: Sophie Farooque, "Thunderstorm Asthma: St Emlyn’s," in St.Emlyn's, June 19, 2021,

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