Alder trees are already blooming and releasing pollen in southwestern B.C., which could be a problem for Olympic athletes and visitors. (CBC)

A Vancouver allergist says the 2010 Olympics will take place at the peak of the West Coast's tree-pollen season, which could present problems for both visitors and athletes.

Olympic athletes need to be particularly careful. Use of over-the-counter allergy and cold medications could lead to disqualification from the Games.

"[February] happens to be the start of our usual tree-pollen season," allergy specialist Dr. Donald Stark told CBC News on Wednesday.

Allergy symptoms can mimic flu and cold symptoms and may cause undue concern among those not familiar with the affliction.

Alder trees produce one of the most significant allergens in southwestern B.C., and with the mild January weather, trees are already emitting alder pollen into the air.

"Even though there may not be very much alder in northern Europe or even Asia, the birch pollen is fairly predominant [there]," Stark said. "People cross-react fairly commonly. If they're sensitive to birch, [they] will start to react to the alder pollen."

Alder pollen can also trigger asthma attacks in people with an allergy, Stark said.

Consumption of some allergy medications containing ingredients like pseudoephedrine can lead to suspicions of athlete doping. (CBC)

Olympic athletes can still take medicine containing pseudoephedrine, a common ingredient in allergy medications, but levels cannot exceed 150 micrograms per milliltre of blood.

"If someone has allergy symptoms and normally takes a decongestant, they could get into a problem with a positive doping test," said Dr. Bob McCormack, chief medical officer for the Canadian Olympic team.

One of the best known cases of inadvertent doping involved Canadian rower Silken Laumann, who had to give up her gold medal at the 1995 Pan Am Games after taking an over-the-counter decongestant to treat an allergy.

The implications of that incident are still top-of-mind for McCormack.

"We sit down individually with each of the athletes and go over every medication they're taking," McCormack said.

"The athletes are very attuned now that if they're going to start anything new — if it's over-the-counter — they check with their team doctors."