Climate Corner: Climate change makes allergies worse

Cynthia Burkhart

“Leaves of three, let it be!” I first learned this little rhyme many years ago, when I was a Brownie Scout in my cute little brown uniform and dark brown beanie hat. Of course, there are many plants with three leaves out in the woods that are quite harmless, but the rhyme is referring to one plant you really don’t want to touch — the dreaded Poison Ivy. Poison Ivy has three glossy deep green leaves on each stem, and can creep on the ground, grow upright, or climb up trees, where it can get quite massive. Contact with any part of the plant, any time of the year, can cause an allergic reaction resulting in a painful rash, blisters, and itching in 80 percent of people.

If you have had a case of poison ivy rash in recent years, and thought it seemed worse than ever before, you are probably right! A six-year study conducted by Duke University showed that elevated levels of carbon dioxide (CO2) in our atmosphere causes Poison Ivy to grow faster, grow more leaves, and produce a more potent form of urushiol, the oil agent found in all parts of the plant that causes the allergic skin reaction. Not only is the urushiol more potent, there is more of it. In 1950, when CO2 levels were about 310 ppm, the average amount of the toxic oil per plant was 15 milligrams. Today, with CO2 levels near 420 ppm, it is a whopping 40.9 milligrams!

Poison Ivy is not the only allergy-causing plant that is affected by the changes in our climate. Do you suffer from hay fever (allergic rhinitis) — the congestion, runny nose, and itchy eyes caused by plant pollen? If so, you are not alone. In 1970, about 1 in 10 Americans suffered from hay fever. By 2000, the number had risen to 3 in 10. With today’s U.S. population at over 332,000,000, that means there are almost 100,000,000 hay fever sufferers in the country. Hay fever accounts for over 13,000,000 doctor’s visits a year in the U.S.

So, here is the bad news: hay fever season is getting worse. Due to warmer temperatures and a longer frost-free season, the pollen season is longer, starting about 20 days earlier in the spring, and lasting longer in the fall. According to the Asthma and Allergy Foundation of America, between 1995 and 2011, pollen season lengthened by 11-27 days.

Another effect of warmer temperatures is that trees, grasses, and weeds are producing greater quantities of pollen, with trees seeing the greatest increase. One study of pollen records from 60 U.S. and Canadian cities from 1990-2018 found that allergy seasons now start 20 days earlier, last 10 days longer, and include 21 percent more pollen. Some evidence suggests that rising CO2 levels may be playing a role as well, causing the pollen itself to be more allergenic.

So, don’t touch the Poison Ivy, stock up on anti-histamines and tissues, and if the pollen is really getting to you, wearing a mask can help.


Cynthia Burkhart is a concerned citizen, gardener, goat farmer and hay fever sufferer.