Why do some people suddenly become struck by hay fever after years of being symptom-free, asks The Magazine from the BBC.

Pollen counts are soaring as summer reaches its peak, sparking misery for hay fever sufferers.

But while many assume the condition starts in childhood, some adults are experiencing the condition for the first time.

And as Beverly Adams Groom, chief palynologist at the National Pollen and Aerobiology Unit at the University of Worcester explains, there is no way to predict when people who are predisposed to allergies (atopic), may develop the condition.

Theories about whether a more polluted, or more sanitised environment, contribute abound.

Hay fever is an allergy to pollens - the male reproductive parts of plants - and when they come into contact with the tissue inside the nose, they trigger an immune reaction that can cause congestion, sneezing, itching, and a runny nose.

Up to 20% of people in the UK may be sufferers with cases highest among teenagers.

Cases have doubled over the last 20 years with some experts suggesting pollution makes it worse and also that people’s immune systems are not now strong enough to combat it.

Other experts fear there is not enough evidence to confirm this.

Brian Lipworth, professor of allergy and respiratory medicine at the University of Dundee says, suggests that one reason for a rise is that many supposed adult-onset cases were in fact sufferers all along - just that their symptoms started off as too minor to notice.

Whatever the position, it will be little consolation to those suffered hay fever right now.