The sum may be greater than the parts for people who suffer a double whammy of taking in smog and pollen, allergists say.

They're now using the term "smollen" to describe those who feel sick not just from pollen allergies, but also air pollution that is traditionally linked to respiratory or cardiovascular problems.

• INDEPTH: The dirt on smog

Dr. Ross Chang says smog makes airways more irritable to allergy sufferers. (CBC)

A national survey of allergy sufferers found one-quarter of those living in urban areas reported their symptoms worsened dramatically in 2005 – a year of record smog alert days in many Canadian cities.

"What smog seems to do is it sensitizes the nose and eyes and upper airways, and makes them more irritable," said Dr. Ross Chang of the B.C. Society of Allergy and Immunology in Vancouver.

Smog makes allergy patients more susceptible to symptoms, added Ross, who treats allergies and helped conduct the survey.

Botanist Rowan Sage says some plants are producing more pollen. (CBC)

Longer pollen season a pest

Smog isn't the only problem pollutant for people with allergies. Some scientists believe increasing levels of air pollution, including carbon dioxide, exacerbate production of pollen in cities.

"You end up with plants growing earlier, they grow faster, they actually produce more flowers, and they produce more allergenic pollen," said Rowan Sage, a botanist at the University of Toronto.

Forecasters say pollution levels will likely stay the same or even rise this summer.

Sonia Khan of Toronto said she's using over-the-counter antihistamines to quell her worsening allergies.

"The whole warrior aspect is trying to figure out and gauge my enemy, which are my allergies," said Kahn, who considers pollen, not other players, to be her adversary while playing tennis. "Where can I conquer them?"

Khan said the allergies worry her, but she won't let them stop her from enjoying a match outdoors.