Now that winter has passed and spring is upon us, you don't have to worry about hay fever right away.

Melbourne's pollen count doesn't even begin until October, and even then the first high pollen day doesn't usually occur until halfway through the month.

But if past years' pollen counts are anything to go by, grass pollen concentrations will get worse throughout spring before peaking in the last week of November.

Hay fever affects about 1 in 7 people, who endure watery eyes, sneezing and itchiness during the spring months.  

From December onwards, the high temperatures burn off the grass and pollen counts trail off.

How do we know how much pollen is in the air? 

This is the machine that does Melbourne's pollen count. 

University of Melbourne botany associate professor Ed Newbigin with the device used to collect pollen data. Photo: Luis Ascui.

For more than 20 years, this Burkard volumetric air sampler has been housed on the roof of Melbourne University's Earth Sciences building .

Built in the 1980s, it draws in air like a vacuum cleaner, capturing pollen and other particles on a sticky glass slide.

The pollen count slides for each day have been kept in storage. This slide is from December 1996. Photo: Luis Ascui.

At 4pm each day between October and December, researchers count the number of pollen grains stuck to the slide, using a microscope.

From this, they can calculate the amount of pollen in the atmosphere and produce a seven-day forecast. If there are more than 50 pollen grains in every cubic metre of air, it is a high pollen day.

So how do we know if it will be a bad year for hay fever?

Historical pollen count data is available from 1991.

Last year was a pretty uneventful year for hay fever. There were just two days with high pollen counts.

The number of high pollen days tends to fluctuate each year and depends on the direction the wind blows and the number of rainy days.

Melbourne University botany associate professor Ed Newbigin, who has been co-ordinating the count for the past 17 years, forecasts a similarly understated hay fever season this year.

He says pollen counts be low because of deficient rainfall over the past few months in Western Victoria and dry conditions expected throughout spring.

It is also looks like there has been a slight trend towards fewer high pollen days in Melbourne over the past two decades. Dr Newbigin says that as the city expands and grassy areas get covered with concrete there is less grass pollen being pumped into the air.

So what causes hay fever?

Curtin University hay fever expert Andrew Crowe says all this spring sneezing is caused by an allergic reaction to pollen and that the types of plant that trigger it differ from person to person.

"The immune system picks up a foreign protein - in this case pollen - and instead of ignoring it, the body thinks it is under attack," he said.

What's in the air?

There are more than 10,000 species of grass in Melbourne - some more allergenic than others - and each of them produces pollen at a different stage of the year.

On top of this, both native and introduced tree species are flowering and releasing pollen at this time of year. Some of these trees tend to trigger people's allergies more than others.

Unfortunately, this biodiversity isn't captured by the pollen counts, which groups all grass pollen together. Dr Newbigin says it is hard to tell these different grass pollen variations apart, even under the microscope.

But he says there are hopes to use DNA sequencing to work out what exactly is in the air and at what concentration.