Page last updated at 08:28 GMT, Monday, 28 June 2010 09:28 UK

Why do adults suddenly develop hay fever?

Man blowing nose

WHO, WHAT, WHY?
The Magazine answers...

Hay fever season is well under way, meaning misery for millions of people across Britain. But why are some people suddenly struck by the condition after years of experiencing no symptoms?

With pollen counts soaring, hay fever sufferers are in the midst of their annual bout of summer misery.

But although the condition is generally assumed to begin in childhood, some adults will be getting a nasty shock as they experience unpleasant symptoms such as sneezing and itching for the first time.

THE ANSWER
Despite plenty of research, no-one really knows
It could be that something in the environment of those with a genetic predisposition to allergies that sets it off
Alternatively, sufferers possibly experience very mild symptoms that they do not notice as children

Unfortunately, there is no way to predict when people who are atopic - that is, genetically predisposed towards allergies - begin to show signs that they are sufferers, says Beverly Adams Groom, chief palynologist at the National Pollen and Aerobiology Unit at the University of Worcester.

But broader theories about whether pollution or, conversely, a more sanitised environment could be causing a rise in hay fever symptoms could offer a clue.

"Lots of people assume that everyone with hay fever develops it in childhood, but we've had people coming to us in their 70s who've just been diagnosed," says Ms Adams Groom.

"People who have a genetic disposition are going to develop it, but as to what triggers it we don't know."

Bee collecting pollen
The bee may love pollen... but hay fever sufferers certainly don't

Hay fever is an allergy to pollens - the male reproductive parts of plants - from grasses and trees.

When these come into contact with the tissue inside the nose, they trigger an immune reaction that can cause congestion, sneezing, itching, and a runny nose.

Between 15 and 20% of people in the UK are thought to be affected, with the numbers being even higher among teenagers and symptoms typically peaking in people's 20s.

However, not all follow this pattern, and Ms Adams Groom suggests this could be linked with whatever is driving the general rise in hay fever cases.

Allergy specialist Prof Stephen Durham has calculated that the number of sufferers has doubled over a 20-year period.

"There's some evidence that pollution exacerbates it," he says. "And you've also got the hygiene hypothesis - that our bodies aren't as strong because we aren't exposed to infections when we are small children that our systems rebel against."

Oddly, researchers in Austria have also found that young children in regular contact with farm animals are less likely to develop allergies later in life.

WHO, WHAT, WHY?
Question mark floor plan of BBC Television Centre
A regular part of the BBC News Magazine, Who, What, Why? aims to answer some of the questions behind the headlines

Children living on farms were found to be three times less sensitive to hay fever and nearly four times less likely to suffer from asthma than those living in a non-rural environment.

This all may suggest that something about modern lifestyles may be responsible.

But, as Brian Lipworth, professor of allergy and respiratory medicine at the University of Dundee says, not enough work has been done to be sure either way.

However, he suggests that it could just be that many supposed adult-onset cases were in fact sufferers all along - just that their symptoms started off as too minor to notice.

"The data sets just aren't there to establish anything," he says.

"I'm suspecting that teenagers may not report symptoms because they are so mild, and it's not until they get to a certain level that they are any the wiser - but we just don't know."

It will, of course, be of little comfort to those currently plagued by itchy eyeballs and streaming noses. But the subject is surely a doctoral thesis waiting to happen.


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