The US allergy season is rapidly increasing, with three extra weeks of pollen season compared to the 1970s. A study by Climate Central found that 173 large U.S. cities gained an average of 21 more days above freezing compared to half a century ago due to increased warmth, which allows plants to bloom longer and produce more pollen. The Centers for Disease Control and Prevention estimates that 25% of adults and 20% of children are dealing with seasonal allergies, causing them to experience longer periods. The Northwest saw the most significant increase in pollen days, with Reno, Nevada, with 100 additional frost-free days. The longer allergy season can lead to breathing problems, increased medication costs, and strain on health care systems, particularly for children and older adults.