Strong downdrafts and dry, cold outflows distinguish thunderstorm rain from frontal rain.
In particular, fungal spores such as Alternaria, have been implicated in asthma epidemics associated with thunderstorms.
The prerequisites for the phenomenon of thunderstorm-related asthma are:
1) a sensitized, atopic, asthmatic individual
2) prior airway hyperresponsiveness before a sudden, large allergen exposure
3) a large-scale thunderstorm with cold outflow occurring during an allergen season in which large numbers of asthmatics are outdoors
4) sudden release of large amounts of respirable allergenic fragments, particularly fungal spores such as Alternaria.
Alternaria sp. Image source: Wikipedia, CDC, public domain.
Alternaria is a genus of ascomycete fungi that are major plant pathogens. They are also common allergens in humans.
Allergens and thunderstorm asthma. Nasser SM, Pulimood TB. Curr Allergy Asthma Rep. 2009 Sep;9(5):384-90.
Thunderstorm asthma. Taylor PE, Jonsson H. Curr Allergy Asthma Rep. 2004 Sep;4(5):409-13.
Thunderstorm asthma in Australia. MJA, 2011.
Explainer: What is thunderstorm asthma? http://goo.gl/k0AIy
Image source: A typical thunderstorm. Wikipedia, Bidgee, Creative Commons Attribution 3.0 Unported License.