Pollen counts are rising. Here's which cities will be hit the hardest

'Tis the season for itchy eyes and runny noses.

With spring in full force, pollen counts are rising around the country, leaving those affected by seasonal allergies little reprieve.

It's estimated that more than 80 million Americans experience seasonal or environmental allergies, according to data from the Allergy & Asthma Network.

Pollen usually comes from trees in the spring, grasses in the summer, and weeds in the fall. It can cause seasonal allergies, also known as allergic rhinitis or hay fever, with symptoms such as sneezing, congestion and watery eyes, according to the National Institute of Environmental Health Sciences.

But the severity and timing of the year's pollen vary by area. Here's what to know about pollen season, so far.