Tree pollen has swept through Calgary's streets, dusting the city in yellow. According to Calgary allergy and clinical immunology specialist Dr. Joel Doctor, it's the pollen you can't see that makes you sneeze.

A: Right now we are in the middle of the tree pollen allergy season, and because the weather's been very, very nice over the last few weeks, we've had a really strong start to the allergy season.

We've seen massive amounts of pollen all over cars and the ground — at times, if you look at spruce and elm trees, you'll literally see pollen flying like yellow dust out of the trees and settling on the ground. And that's what everyone is seeing and noticing.

A: Most of the yellow pollen is from the pine and spruce trees in the area — and that pollen tends to be very heavy and very sticky. That pollen is released from those trees and doesn't go very far — it tends to sink to the ground and stay until it's washed away by the rain.

At the same time, there's other pollens being released by other trees, such as birch trees, which is very, very small — we're talking particles maybe 75 microns in size. And particles that size, they stay airborne for long periods of time, and can travel very great distances, and it's those particles that cause hay fever.

A: For the most part, no — because it doesn't stay airborne very long. It tends just to fall to the ground and stick.

But at the same time, there are other trees that are pollinating that are causing a lot of hay fever. In the Alberta region, birch trees are the most common cause of springtime hay fever and people are getting hit very hard by that.

There's pollen from other trees that accumulates as well but most of that is from pine trees and spruce. And there's other trees pollinating as well, like cottonwood and poplars. They all contribute to that.

Once tree season winds down over the next week or so, we head into grass allergy season — and we're not going to see a lot of that yellow stuff on the ground during grass allergy season, that in fact is a stronger allergy season for most Albertans.

A: It's the northern pasture grass and we're surrounded by those grasses, and their pollens travel huge distances and they cause an awful lot of hay fever.

That tends to start ramping up in early June, peaking usually around Stampede time — early July is the peak for the grass allergy season, then it winds down later in July, then in August and September, the allergy season tends to wind down a lot.

A: For people being affected by this, the logical first thing to do is take a really good over-the-counter, non-sedating, antihistamine — that would be good first-line treatment and it would be good for alleviating the symptoms of itching and sneezing.

A: That's an option if it's really quite bad … and you're suffering quite terribly, it's a great day to go see a matinée — the air conditioning in the shopping centre is fantastic.

The worst thing to do is spend a lot of time in the wind, on a hot, dry, windy afternoon, riding a bike for example. Being outside entails a much higher level of exposure, and patients will suffer.

A: Right now I'd say it's actually stronger than average, largely because it has been very dry, and quite warm over the last couple of weeks. So we've had very high tree pollen counts. If this weather pattern continues, then we'll likely have a stronger than average season into June and July as well.

When it rains, then pollen tends to be taken out of the air, so rain is really an excellent reprieve for allergy sufferers.

It will [also] give us a break between the tree pollen season right now and the grass allergy season that's about to start — so these patients will get a bit of a break between the two seasons.

A: There's only about 25 per cent or so of the population that has any kind of seasonal allergy symptoms — and that's a combination of factors, including a genetic predisposition to develop allergies.

There are some people who can hang around pollens and animals and peanuts — and they never develop allergies. They're just not genetically prone to do so.

Of course you cant pick your parents. This stuff is genetic — it's always a package deal — but again, for the most part, it's very controllable. And manageable.