Dry, windy days. Wind blows pollen into the air, increasing hay fever symptoms. If you have pollen allergies, shut the windows and stay indoors on windy days.
Rainy or humid days. Moisture makes mold grow, both inside and out. Dust mites also thrive in humid air. However, if you're allergic to pollen, humid or damp days are good. The moisture weighs down the pollen, keeping it on the ground.
Cold air. Many people with allergic asthma find cold air a trigger -- especially when exercising outside. It impacts the airways, causing a coughing fit.
Heat. Air pollution is worst on hot summer days. Ozone and smog in the air can be a serious trigger for people with allergic asthma.
The change of seasons also has a big effect on allergies.
Spring. In cooler states, plants start to release pollens in February or March. Tree pollens are a common spring trigger for people with allergies.
Summer. Early in summer, grass pollen can trigger symptoms. Later in the summer, ragweed and other weeds can become a problem. Mold can hit its peak in July in the warmer states.
Fall. Ragweed season usually ends with the first frost in October. In colder states, mold tends to be worst in October.
Winter. Indoor allergens -- like pet dander and dust mites -- can become more a problem in winter. Why? When it's cold out, you spend more time indoors.