The pollens and molds that cause hay fever are lightweight and can be blown around by the wind. Ragweed pollen has been found 400 miles out at sea and two miles up in the air. Pollen also tends to rise in the day when the air is warmest and fall in the evening as the air cools down.
Moving from an area where there is an allergy trigger will not usually work. Pollen is everywhere on the planet, even the Antarctica. A person who is prone to hay fever will often develop an allergy to a new species if he moves away from the original trigger.
The pollens that cause hay fever generally come from trees, grasses and weeds, with ragweed being the most common of all. The sticky pollens of colorful flowering plants do not generally cause allergies because they are less likely to fly around in the air.
In North America, trees tend to be a problem for allergic rhinitis in the early spring before their leaves unfold. This is usually from early March to late May.
It will depend on where one lives in North America. The northern United States and Canada will have a later spring, so the hay fever season will start later.
Grasses, in North America, are generally a problem for hay fever sufferers from about June until mid-August. In some warmer climates the grass season can last up to six months.
Again, the start time and duration of the season will depend on where an individual lives.
Weeds will generally be an issue from mid-August until October or early frost. The most common weed for hay fever is ragweed. It actually causes up to 75% of seasonal allergic rhinitis.
As with trees and grasses, the season will vary depending on which part of North America the individual calls home.
In the United States, no area or state is totally free of ragweed. In Canada, there isn’t any ragweed in Newfoundland, and only a little in British Columbia or the Prairies, except for an area around Winnipeg. The worst area for ragweed in Canada is known as “ragweed corridor.” It stretches from Windsor, Ontario to Quebec City, Quebec.
Molds can be a problem for allergy sufferers all year-round. They are hardier than pollens, and so they can live in much colder temperatures. They survive well in damp, warm air, and are plentiful around the shores of lakes and rivers. They are not common in deserts.
Molds can also move indoors and live in damp parts of the house, such as the bathroom, basement or cluttered closets. This can create a problem for the whole year.
If an individual suffers from hay fever, he/she will need to be aware of the season for his/her particular triggering pollen. This will require researching the growing season of the region and noting when the allergic rhinitis symptoms spike.