Blame springtime allergies on pollen. If symptoms kick into high gear early in the season, trees such as ash, elm, maple, birch, poplar, beech, walnut, sycamore, cypress, hickory, pecan, cottonwood and alder are your usual suspects. Allergies that strike later in the season are most often due to the green stuff under your feet. People who are allergic to one type of grass are usually susceptible to them all. Either way, when the ground starts to thaw and the weather warms up, spring allergy season is in effect --- which means the warmer the region, the sooner it strikes. NEXT: Where to go, and where not to go, if you're allergic to grass and pollen.