Early or Late Spring Blooms? Both Affect Asthma

Spring is a time for blooming plants–and pollen. This image shows poppies blooming in California in Spring 2020. (Source: NASA Earth Observatory)

From Wisconsin to Washington D.C., pollen counts were quite high this spring, making seasonal allergies brutal for many people. Recent research shows that changes in the onset of spring—both early and late—can extend allergy misery and lead to more severe asthma for some people.

Warm springtime temperatures signal shrub buds to burst, trees to leaf-out, and flowers to bloom. As plants produce and release pollen, our bodies can mistakenly identify it as a dangerous intruder to our respiratory systems. Our immune systems produce chemicals to fight it, inducing sneezing, watery eyes, and stuffy noses. Research also shows allergenic pollen is also among the leading risk factors known to worsen asthma.

Amir Sapkota, a professor of public health at the University of Maryland, and his colleagues investigated how changes in the timing of spring onset affected asthma hospitalizations in Maryland over the past decade. The team used the Normalized Difference Vegetation Index (NDVI), which shows the relative “greenness” of vegetation, to determine the timing of the spring onset. (The data come from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua and Terra satellites.) The team combined the satellite data with pollen counts and inpatient hospital admissions from the Maryland Department of Health.

They found that very early onset of spring (10 days early) was associated with a 17 percent increase in asthma hospitalizations in Maryland from 2001-2012, while late onset (3 days later) was associated with a 7 percent increase.  

The graph shows the changes in pollen season length for birch, oak, and poplar trees in relation to the start of spring.

Sapkota explained that the hospitalization risk increased because of changes in pollen dynamics. Tree pollen is common in spring, while grass and weed pollen are more common during summer and fall. According to Sapkota, an early onset of spring leads to earlier and longer tree pollen seasons. At the other end, late onset causes different species of trees to bloom at the same time, thus increasing overall pollen levels in the environment. Both scenarios can lead to increases in asthma hospitalizations.