As the leaves begin to fall, do your allergy symptoms start to rise? More than 36 million Americans experience seasonal allergies, according to the American Academy of Allergy, Asthma and Immunology (AAAAI). For many people, fall is the worst time of year for symptoms such as frequent sneezing, runny nose and red, watery eyes.

Ragweed is the most common fall allergen, according to the AAAAI. People living in the Northeast, Midwest and South are most likely to encounter ragweed, a yellow flowering plant often found in fields, along roadsides and in vacant lots.

Avoiding ragweed is no easy task. Each ragweed plant produces 1 billion grains of pollen throughout its lifetime. Pollen is the small, powdery substance of a flowering plant involved in fertilization.

These grains are so lightweight that they can travel up to 400 miles. A person who sneezes in Kansas City may have a single ragweed plant in Peoria, Illinois, to thank for the experience.

Other weeds that may cause fall allergies include:

• Amaranth
• Cockleweed
• Dock
• Mugwort
• Pigweed
• Tumbleweed
• Sagebrush

Outdoor molds are another frequent source of fall allergies. They are found in places such as fallen leaves, soil, rotted wood and rain gutters. Regions with damp falls also are susceptible to the growth of mold inside the home, especially in kitchens, bathrooms, basements and carpets. Like pollen, mold spores easily travel through the air.