A new study by the University of Utah published in the journal PNAS found that pollen seasons have been getting longer and more intense in North America over the last 30 years, aggravating asthma and weakening defenses against respiratory viruses, resulting in more emergency room visits that disrupt lives. Researchers comparing pollen metrics between 1990 and 2018 from 60 monitoring stations indicate that seasons are starting up to 20 days earlier and lasting up to eight days longer, affecting millions of allergy sufferers. The study looked at variable factors such as temperature, rainfall, frost days and carbon dioxide concentrations, and found that an increase in mean annual temperatures was the strongest driver. According to the U.S. Centers for Disease Control and Prevention, about 19 million adults have been diagnosed with hay fever, an allergic reaction to pollen, a fine powder from plants that can come into contact with the eyes, nose, mouth and throat.