The annual reprieve from pollen-induced hay fever symptoms is getting shorter and some lay the blame on changing weather patterns.

Weather is also behind the big increase in the number of people suffering from hay fever, some scientists believe.

One theory suggests it is causing plants to be stressed and as a consequence they are producing stress proteins which have been found to be highly allergenic.

Late rains and more humidity were also having an effect, according to Australasian Society of Clinical Immunology and Allergy president Richard Loh.

"There are certain pollens that are not very allergic but when you get late rain like we have been getting, the rain makes certain flowers burst and release much smaller pollen and that then becomes much more allergenic," Dr Loh explained.

"Everyone is saying things are really bad in the past couple of weeks and, although we don't know the real reason, it may be the fact that we are getting rains and then we are getting two to three summery days."

Other factors believed to be affecting hay fever rates include the growing popularity of olive tree plantations, the pollen of which is a known allergen for many people.

Rag weed was also a cause for concern, according to Lung Institute of WA medical director Philip Thompson.

Rag weed pollen causes big problems in the US, to the extent that signs about rag weed season are found on interstate boundaries warning those who are allergic.

"It is a big deal in the US and a lot of the practice of allergists in the US is dealing with people who are rag weed allergic," Professor Thompson said.

It was traditionally held that rag weed was not present in Australia. However, Professor Thompson said it had been sighted and that 10 per cent of people included in a recent survey at his clinic tested positive to rag weed allergies, indicating that they had been previously exposed to the allergen.

Dr Loh said little was known about pollen counts or mould, which can also cause allergic reactions, in WA because a new allergen survey had not been done for 20 years.

"There is no research done on native pollen, there is no manufacture of desensitisation for native pollens, the manufacturers overseas are all northern hemisphere so we don't have a local company that can provide us with native pollen to test," he said.

But it is not just plant pollens being affected, certain tropical moulds are also known allergens and can cause severe sinus disease as well as lung disease and asthma.

"With climate change we are seeing more tropical low patterns coming into Perth from the north, my concern is we might begin to see more tropical mould-induced allergic disease," he said.

Professor Thompson said for those people who were pollen and house dust mite allergic their yearly reprieve from symptoms was shortening.

The normal hay fever season seemed to be extending into January and February because the air was not so hot and dry which meant grasses were not dying off as quickly.

Professor Thompson said house dust mites, which thrive between June and December in the indoor humidity created by rain and indoor heating, were also surviving longer.

"We are seeing people present with mite and grass pollen allergies in the summer months which we never used to see before, which is a direct by-product of changing weather patterns," he said.

The West Australian

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