If you have hay fever, you're probably allergic to pollen. Pollen is released by some plants and looks a lot like dust.

Here are some of the plants that are most likely to cause hay fever.¹

• Weeds: ragweed, English plantain (also called ribgrass or ripplegrass), lamb's quarters (a common weed), pigweed, Russian thistle (tumbleweed), sagebrush.
• Grasses: Bermuda grass, Johnson grass, Kentucky bluegrass, orchard grass, redtop grass, sweet vernal grass, Timothy grass.
• Trees: ash, box elder, elm, hickory, oak, mountain cedar, pecan.

Common plants that cause hay fever are (from left to right): tumbleweed, ragweed and Timothy grass. (Photos from the American Academy of Allergy, Asthma and Immunology.)

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.