Pollen is about to peak in Philly. Here’s what to know about the green snow season.

April is about to yield to May on a glorious note, with the azaleas blooming and the trees swollen with the fresh greens of spring under a sun that will warm temperatures well into the 70s.

And the forecast couldn’t be worse for hundreds of thousands of allergy sufferers in the Philadelphia region.

Actual pollen counts are getting scarcer these days, but allergists say they don’t need slide specimens to know that the stuff that looks like so much green snow on cars and other surfaces has been coming after their patients.

Being asked if this season is particularly brutal is a rite of spring, said Corinna S. Bowser, allergist with Bryn Mawr Medical Specialists. That’s due in part, she says, to the fact that patients have just survived a pollen-free winter and are caught unaware.

But in this case, she said, yes, this has been a rough start to the annual pollen festival.

The run of generally dry days in the last two weeks may have been great for outdoor activities, but it has also been a bonanza for tree-pollen flight. As a rule, if humans like the weather, so will those miniature tormentors that are part of a tree’s reproductive efforts.

“Spring 2025 has been a particularly difficult season for those who suffer from seasonal allergies,” said Manay N. Segal, with the Chestnut Hill Allergy & Asthma practice.

Unfortunately, it’s likely about to get more severe. Based on historical data, the trees should be approaching their annual peaks, just as the grass pollen population is poised to increase.

In the next week or two, the air may be full with equal amounts of grass and tree pollen, said Marc Goldstein, allergist with the Center City Asthma Center.

» READ MORE: Pollen season is underway in Philly. Here’s why pollen is so hard to predict and track.

With little consequence to the majority of humanity, the microscopic pollen grains that are the seeds of the next generation for trees, grasses, and ragweed fill the air more or less from the spring to fall equinoxes.

But for more than 80 million people in the United States, by the Centers for Disease Control and Prevention’s estimate, pollen is perceived as an invader, prompting the body to release chemicals that can trigger sneezing and eye irritations.

For asthmatics and other people with respiratory conditions, the reactions can be more than annoyances.

On average, the tree-pollen season peaks right about now and continues into early May, when the grasses join the party. The pollen fest backs off by mid-June, but several weeks later, the ragweeds emit their emissaries.

Pollen has been pestering humans since trees and noses have coexisted on the planet. In all likelihood, the fans filling the Roman Colosseum did their share of sneezing: Among the more famous seasonal-allergy sufferers was Caesar Augustus.

But it was not until the late 19th century that pollen was identified as the agent provocateur by British physician Charles H. Blackley. He suffered a sneezing fit one day when a passing carriage kicked dust in his face. He collected dust samples, examined them under a microscope, and the guilty pollen grains revealed themselves.

Evidently, yes, not only in terms of duration but also in the swelling ranks of sufferers.

“What I have noticed and what the statistics bear out is that a greater percentage of the population now report having seasonal allergies,” Segal said.

Various research documents that the incidence of seasonal allergies has more than doubled since 1970.

No one is quite sure why, but one possible explanation for the bumps in developed nations could be the so-called hygiene hypothesis, a term that appeared in 1989 in a paper by a British epidemiologist.

He speculated that people who lived in rural areas and interacted with nature might have stronger immune systems and thus be less prone to allergic reactions.

Other research has suggested that pollution, particularly ozone, might be interacting with pollen in such a way as to make it more dangerous to respiratory seasons.

And the seasons appear to be starting earlier and lasting longer, the result of a warmer, wetter world and increased carbon dioxide that is a bonanza for plant life.

Rain is the sufferer’s friend, since it inhibits pollen flight. For the allergic, rain may be a wild card in the global-warming equation, Estelle Levetin, a Tulsa University professor emerita and aerobiologist, has said.

Plants may be producing more pollen, but a wetter atmosphere and more rain would mean fewer punitive days for allergy-sufferers.

However, rain relief in Philadelphia has been scarce the last two weeks. Showers are in the forecast for later in the week, but the next two days are expected to be warm, dry, and ever-so pollen friendly.

Allergists advise trying to stay inside when pollen counts are high. Unfortunately, the region no longer has a certified National Allergy Bureau counter, but the Asthma Center in Center City posts daily automated counts around 7 a.m.

With the caveat that no one has yet developed a reliable way to forecast pollen, it doesn’t hurt to consult the pollen.com outlooks, which rely heavily on weather conditions and can be useful indicators for what’s to come. Its outlook for Wednesday for the region, by the way, calls for extreme pollen levels.

Consult your car hood, trash can, or window. If you’re seeing the green snow, take heed.

Otherwise, beyond taking medications, allergists advise:

Only 235 days until winter.