Asthma epidemics associated with some thunderstorms have been found to contribute significantly to the number of hospital attendances for asthma given the appropriate meteorological conditions. The environmental changes found to be important are a sudden change in air temperature and a sudden rise in grass pollen concentration. Individuals who are affected are more likely to have a history of hayfever and much more likely to be allergic to rye grass; they are also less likely to be taking inhaled corticosteroids at the time of the thunderstorm.

The mechanisms behind thunderstorm asthma are not well established as it is caused by a combination of many factors. However, thunderstorms are known to have a marked effect on pollens, fungal spores, as well as dust and smoke particles. Although representing a small proportion of airborne particles present in the atmosphere, pollen grains can be causative agents of allergic respiratory responses in individuals who are allergic to pollens. Some grass allergen (for example, ryegrass allergen) is located on the surface of starch granules within pollen grains. A single pollen grain contains up to 700 starch granules of 0.6 to 2.5 um (small enough to reach the lower airways in the lung). When it rains or is humid, pollen grains can absorb moisture and burst, releasing hundreds of small allergenic particles that can penetrate deep into the small airways of the lung. It is also thought that an increased release of fungal spores may occur after a thunderstorm or heavy rainfall, thereby precipitating asthma. According to a study carried out by Celenza et al (1996), based on the asthma epidemic, which occurred in London on 24 and 25 June 1994 after a thunderstorm, it was noted that lightning strikes, rainfall, drop in air temperature, air pressure, and humidity seemed to be related to the onset of the asthma epidemic.

According to D'Amato et al (2007), the characteristics of described epidemics of thunderstorm-associated asthma can be summarized as follows:
1.A link exists between asthma epidemics and thunderstorm.
2.Epidemics related to thunderstorm are dependent on seasons when there are high atmospheric concentrations of airborne allergenic pollens.
3.The start of the thunderstorm has a close temporal association with the onset of epidemics.
4.Subjects with pollen allergy, who stay indoors with closed windows during thunderstorm, are not usually affected.
5.Subjects who are not under correct anti-asthma treatment are at a major risk whilst subjects with allergic rhinitis and those without previous asthma can experience severe bronchoconstriction (constriction of the bronchial air passages).

Precautions to take in the event of a thunderstorm
1.Watch out and listen closely for weather reports.
2.Be aware that thunderstorms could trigger your asthma.
3.Increase you preventer inhaler, in consultation with your doctor or nurse, and seek medical attention if you experience an extreme attack.
4.Keep a close eye on your condition either by taking regular peak flow readings or recording your symptoms.

References
1.Venables KM, et al. Thunderstorm-related asthma - the epidemic of 24/25 June 1994. Clin Exp Allergy 1997; 27: 725-736.
2.Wark PAB, Simpson J, Hensley MJ, Gibson PG. Airway inflammation in thunderstorm asthma. Clin Exp Allergy 2002; 32: 1750-1756.
3.Celenza A, Fothergill J, Kupek E, Shaw RJ. Thunderstorm associated asthma: a detailed analysis of environmental factors. BMJ 1996; 312: 604-607.
4.Campbell-Hewson G, Egleston CV, Sherriff HM, Robsinson SM, Allitt U. Epidemic of asthma possibly associated with electrical storms. BMJ 1994; 309: 1086-1087.
5.D'Amato G, Liccardi G, Frengueli G. Thunderstorm-asthma and pollen allergy. Allergy 2007; 62: 11-16.

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