That heavy dusting of yellow on your car hood and your itchy eyes should have warned you: Tree pollen has spiked to “very high” levels in the Washington area this week.

“The yellow dust is oak and pine,” said Susan Kosisky, co-chief of Walter Reed Army Medical Center’s Allergen Extract Lab, which tracks pollen counts daily. “When they come out together, that’s when the air gets saturated. It’s very sticky.”

Allergy sufferers are well aware that the spring festival of pollen has opened. The seasonal high of 2,302 grains per cubic meter was recorded Tuesday, and the peak pollen count usually comes just about now, between April 16 and 26, Kosisky said.

“Very high” means that “almost all allergy sufferers will experience symptoms; those extremely sensitive could have severe symptoms,” according to the National Allergy Bureau.

Unlike last year, when tree pollen levels skyrocketed in early April, “this year has been up and down, up and down, up and down,” Kosisky said. Rain helps clean the air, but it also encourages blooming. There’s also been a slight upward trend in tree pollen levels during the lab’s 13 years of observations.

This is not just an annoying rite of spring. It can be dangerous to people’s health, too.

“For people with allergic asthma, this can have life-threatening consequences,” said Mike Tringale, a spokesman for the Asthma and Allergy Foundation in Landover. “For those that just have the upper-respiratory allergies, it’s generally not life-threatening, but it’s severe quality-of-life-threatening.”

About 25 million Americans have allergic rhinitis; and for the 10 million more with asthmatic allergies, missed work days and hospital visits cost more than $32 billion annually in direct health-care costs and lost productivity, the foundation estimates. Costs for individuals include not just pharmaceutical prices, but also lost hours of sleep and decreased alertness.

A foundation report issued last year with the National Wildlife Federation concluded that global warming may be increasing the number of allergies people deal with because a longer and hotter growing season prompts plants to produce more pollen. The Washington area is usually one of the top 25 to 50 most-challenging places to live for allergy sufferers, although Tringale said those numbers depend on weather patterns.

“Allergies are bad everywhere,” he said.

Michael R. Kletz, a board-certified allergist who practices in Manassas, said he’s hearing this week from plenty of patients, including some new ones who either just realized they have allergies or whose over-the-counter medications no longer work.

“We’re seeing lots of patients with allergic rhinitis, which you can call hay fever,” he said. “The symptoms range from runny nose to watering eyes, to wheezing and asthma for some.”

Henry Fishman, a Chevy Chase allergist, said the severity of the pollen season depends on how much snow or rain occurred in the previous winter and the proximity of blooming plants. “We’re in such a beautiful city, with all these flowering trees,” he said.

The best remedy, short of a doctor’s visit, is to stay indoors with the windows closed when pollen counts are high or shower when coming in from outdoors, experts said. Over-the-counter antihistamines work for some people, but Fishman said patients should be careful about taking medications that contain decongestants because they can be dangerous for those with high blood pressure or other conditions.

Of course, trees eventually stop pollinating. But that opens the season for grasses and weeds, and they’ve started to blossom.

“There’s something for everyone,” Kosisky said.

Jason Samenow of the Capital Weather Gang contributed to this report.