You would think that rain clears the air and brings relief for hay fever sufferers. But the opposite can be true: during and after a thunderstorm, hay fever and asthma symptoms can actually increase significantly. This phenomenon is called thunderstorm asthma and can cause serious breathing difficulties even in people who normally only have mild hay fever.
Medical warning: thunderstorm asthma can cause acute breathlessness that requires emergency medical help. In case of severe breathing difficulty: call 112.
How does thunderstorm asthma develop?
During a thunderstorm, a unique combination of factors comes together:
1. Updrafts
Powerful upward air currents lift pollen grains high into the atmosphere, where humidity is high.
2. Pollen rupture
Due to moisture, temperature differences and electrical charge, pollen grains absorb water and burst open into hundreds of smaller fragments: sub-pollen particles.
3. Downward dispersal
Powerful gusts of wind blow the microscopic sub-pollen particles down to ground level, where people inhale them.
Why are sub-pollen particles more dangerous?
Normal pollen grains are relatively large (20--50 micrometres) and are largely caught by the nose and upper airways. There they cause the well-known symptoms: sneezing, runny nose, itchy eyes.
Sub-pollen particles are much smaller (less than 5 micrometres) and therefore penetrate deep into the lungs, reaching the bronchi and alveoli. There they trigger a powerful immune response: airways swell, produce excessive mucus and the muscles around the bronchi go into spasm (bronchospasm).
Who is at risk?
Hay fever + asthma
People with hay fever and (mild) asthma, even if the asthma is normally well controlled.
Grass pollen allergy
Grass pollen ruptures most easily during thunderstorms. People with grass pollen allergy are at the greatest risk.
Hay fever only
Thunderstorm asthma can be the first time someone without an asthma diagnosis experiences breathlessness.
The Melbourne incident (2016)
The most well-known example of thunderstorm asthma occurred in Melbourne, Australia, in November 2016. A powerful thunderstorm during the grass pollen season caused a wave of thousands of emergency presentations for breathing difficulty. Several people died as a result. This incident made clear worldwide just how dangerous thunderstorm asthma can be.
Thunderstorm asthma in the Netherlands
Although the extreme situation seen in Melbourne is unlikely to occur in the Netherlands, thunderstorms during the grass pollen season (May--August) are common here. When high pollen concentrations coincide with thunderstorms, emergency services report more asthma-related emergencies. PollenAlert.nl displays a thunderstorm warning on the homepage when this combination is current.
What can you do?
Stay indoors
During and immediately after a thunderstorm when pollen pressure is high. Close windows and doors.
Keep medication handy
Take your antihistamine, nasal spray and -- if you have asthma -- your bronchodilator (salbutamol).
Monitor pollen levels
Check the live pollen map and the weather forecast. With high grass pollen + thunderstorms: take extra care.
Call 112 in an emergency
If you experience breathlessness, wheezing or the feeling that you cannot get enough air: seek immediate medical help.