Australia's hay fever sufferers can expect their torment to last longer and become more intense with climate change, according to researchers at home and abroad.

About one in five Australians are affected by hay fever, also known as seasonal allergic rhinitis, with residents of the ACT reporting the highest proportion and the 25-44 age group most affected, according to Janet Rimmer, a respiratory physician and allergist at St Vincent's Clinic in Sydney.

Bombs away: Pollen counts aren't the only things on the rise. Fletcher Youens (left) and Will Martin make a splash at the home of friends Aloysius and Xavier Zadro. Credit:Michele Mossop

"Certainly allergic diseases have increased in the past 10 to 20 years," Dr Rimmer, who is also an associate professor at the Sydney Medical School, told Fairfax Media.

One factor may be the southern spread of pollen-rich subtropical grasses, such as the introduced bahia and Bermuda or couch species, which are also common on sport ovals and nature strips.