Thunderstorms can trigger respiratory problems by causing particles of pollen that are normally too big to enter the airways to explode.

"Thunderstorm asthma is triggered when there is a sudden change in weather conditions," explains Dr Simon Judkins, from the Australasian College for Emergency Medicine.

"The movement from a hot a windy day where there is an increased pollen load in the air to an incoming storm front which adds a lot of moisture to the air will see pollens absorb the moisture, and burst."

"This releases thousands of tiny allergen particles which are then inhaled by people and can trigger asthma attacks."

The phenomenon occurs when moisture-charged winds immediately before a storm whip up pollen.

A high pollen-count day is one with 50 grass pollen grains per cubic metre of air, averaged over 24 hours. Extreme days have 100-plus grass pollen grains per cubic metre of air.

There is a 90 per cent chance of thunderstorms across the Border and North East and Tuesday.

Dr Judkins says people with asthma and other allergy syndromes will be affected - but children and the elderly are very vulnerable

According to the Australasian Society of Clinical Immunology around one in four people with allergic rhinitis (hay fever) also have asthma. Some people with severe allergic rhinitis (hay fever) think that their allergic rhinitis turns into asthma or will make them tight in the chest or wheeze. This is incorrect as pollen can trigger asthma as well as allergic rhinitis symptoms. 

Respiratory physician Megan Howden said thunderstorm asthma can affect people with pre-existing asthma but also those who have hay fever but no previous asthma. "Those most vulnerable are people with asthma which is not well controlled. Others ar risk are those with hayfever and asthma symptoms which occur in spring," she said. "Previous episodes have seen around a 10-fold increase in asthma presentations to emergency."

Dr Judkins agrees. "So many people, for example, will have hay fever, which is an allergy to pollens, but may not have had asthma symptoms. However, in these circumstances, when they are exposed to such a large allergen load which is deposited into their lungs, will have an asthma attack."

Not everyone who gets thunderstorm asthma has had it before. They have normally had severe pollen allergic rhinitis (hay fever) and most have been found to be allergic to ryegrass. Presumably the massive load of small allergenic particles being inhaled straight into the lung trigger these attacks. 

Inhaling the pollen fragments can cause an allergic reaction in the lungs resulting in the sudden onset of symptoms such as shortness of breath, a cough, a wheeze, and chest tightness. 

Thunderstorm asthma feels like your lungs have "tightened up", says Dr Judkins.  "If you have seen anyone who has had an allergy and their lips or eyes swell, a similar thing happens in the lungs. The patient gets 'bronchospasm' and swelling, which makes it harder to breath in and out.

"Think of how you feel when you try to breath in and out through a straw. It's very hard work, very tiring .., and distressing."

The best way to treat thunderstorm asthma is to prevent it occurring, where possible. So good asthma control is essential.

Get help. While some sufferers will have asthma medications with them and will recognise the symptoms and start implementing their asthma plan, this may be a first-time experience for many people. Ventolin spray is the first-line therapy, followed by steroid medication.

Your GP has these medications but, if it is outside their working hours, you may need to head to your nearest emergency department.