The type of pollen that causes allergy symptoms comes from plants (trees, grasses, and weeds) that typically don’t bear fruit or flowers. They make lots of small, light, dry granules that can float in the wind for miles.

Common plant allergens include:

• Weeds: ragweed, sagebrush, redroot pigweed, lamb's quarters, goosefoot, tumbleweed (Russian thistle), and English plantain;
• Grasses: timothy grass, Kentucky blue grass, Johnson grass, Bermuda grass, redtop grass, orchard grass, sweet vernal grass, perennial rye, salt grass, velvet grass, and fescue;
• Hardwood deciduous trees: oak, ash, elm, birch, maple, alder, and hazel, as well as hickory, pecan, box, and mountain cedar. Juniper, cedar, cypress, and sequoia trees are also likely to cause allergy symptoms.