Plants and trees in the neighborhood add to the beauty of the landscape and supply us with fresh oxygen. But, as spring approaches, some trees and plants also fill the air with their pollen causing allergies in many people. Suddenly, everyone suffers from stuffy noses and watery eyes. Exposure to their pollen causes many respiratory problems in adults and children alike.
Plants And Trees That Cause Allergies
It pays to know the plants and trees around you so that you can take precautionary measures to avoid allergies. Here are some common plants and trees that you must watch out for during spring.
1. Oak
Oaks are everywhere, predominantly in the woods around the Coastal Plain from Texas to Virginia, and Florida. Spring is the ideal time for the oaks to release their pollen.
Although oak trees produce less potent pollen, they release it in very large volumes. A study was conducted to assess the relationship between tree pollen (maple, oak, and birch) and over-the-counter daily allergy medication sales in the New York City metropolitan area.
The over-the-counter allergy medication sales increased significantly on the day of a pollen peak for oak, maple, and birch. The increase also persisted for three days after the peak. This data can help experts predict the onset of allergic responses in the study region.1
2. Pecan
The pecan tree is generally found near woods and orchards in abundance in the western edge of the Southeastern United States, north Florida, Georgia, Indiana, and Ohio. This tree also releases its pollen during spring.
The pecan tree is a type of hickory tree that can be as allergenic as ragweed. Oil extracted from pecan nuts is used in numerous products including processed foods, cosmetics, and soaps. Pecan tree pollen is considered so highly allergenic that its pollen is the second most common source of severe allergies after ragweed.
However, more specific scientific data about its role in causing allergic diseases is required. In one study, its pollen grains comprised 70% of the total airborne grains for the month of May. Pecan’s highly allergenic pollen grains are correlated to the incidence of hay fever in the exposed population and are a major cause of the development of asthma in children.2
3. Ragweed
Ragweed is most commonly seen near fields, riverbanks, roadsides, and rural areas of the Midwest and in the Mississippi River basin. The plant releases its pollen during summer and fall.
Ragweed is by far the most allergenic plant and according to the Asthma and Allergy Foundation of America, 75% of people with pollen allergies are allergic to it. The plant is extremely common and there are 17 types of ragweed in North America.
It is less common on the West Coast and hence there is less pollen in those areas. In the recent National Health and Nutrition Examination Survey (NHANES) III (1988-1994), 26.2% of the US population was sensitized to ragweed, the third most common allergen after dust mites (27.5%) and perennial rye grass (26.9%).3
4. Rye Grass
This variety of grass is usually found in lawns, meadows, and pastures all over the northern parts of the United States. Its pollen is released during spring and summer.
Though all types of grasses are allergenic, some such as the rye grass are double trouble to those who suffer from allergies. When grass is mowed, you pick up mold as well as its pollen. Rye grass pollen has been considered a major sensitizing agent in patients with pollinosis.
It is capable of producing a great amount of pollen. In a dry atmosphere, pollen may remain stable for centuries! Estimates suggest that a hectare of a rye-grass can produce up to 100 kg of pollen and that a gram of this pollen can contain around 100 million grains.4
5. Maple
The maple tree, whose leaf is seen on the Canadian national flag, is commonly found along streams and in woods of the eastern United States and Canada. Its pollen is released during early spring.
The ash-leaf maple or box elder tree produces potent allergens that affect many people. In a study, 371 allergy patients were tested for hypersensitivity towards prevalent tree pollen in the areas surrounding New York between 1993 and 2000.
The study noted that in the New York City area, hypersensitivity to tree pollen most often is manifested with an allergy to maple, oak, and birch tree pollen. In Cincinnati, the pollen from maple had a significant impact on asthma-related hospital visits.5
6. Elm
The elm grows commonly around cultivated wetland habitats of Eastern and Midwestern United States. The pollen of the American Dutch elm is released during spring and the lace bark elm releases its pollen during fall.
Just like other allergenic plants and trees, the elm produces flowers and fruits that release pollen into the air. Though around 100 million elm trees died due to the Dutch elm disease between 1930 and 1980, the trees recovered and made a comeback in the late 1990s.
In young children, the presence of aeroallergen sensitivity may serve as a risk factor for the development of persistent asthma. Concomitant aeroallergen sensitivity is frequently present in both chronic upper and lower airway diseases and is additionally associated with severity of rhinitis and asthma in children.6
7. Mountain Cedar
This tree is mostly found in mountainous areas of Arkansas, Missouri, parts of New Mexico, Oklahoma, and Texas, and it releases its pollen during spring.
Mountain cedars cause some of the most severe allergy symptoms. Hypersensitivity to mountain cedar pollen causes severe seasonal allergic disease in broad areas of the south-central US and northern Mexico. Related species within the cedar family also cause similar problems worldwide.7
Many people oppose cedar trees as it absorbs a lot of ground water, especially in areas that have water shortages. They produce pollen in such large quantities that it often prevents people from enjoying outdoor activities.
8. Mulberry
Mulberry trees are predominantly found in woods and river valleys of the Eastern United States. It releases its pollen between winter and summer.
Although not native to the US, the mulberry has been known to contribute to hay fever. They were imported to the United States from China to establish the silkworm industry. Mulberries produce flowers and fruit, and the flower’s pollen is wind-borne and highly allergenic.
In one study, sensitization to mulberry and other trees was present in young children. Data from the study shows that many children with allergic rhinitis living in the Great Basin were sensitized to an outdoor allergen by as early as 2 years of age.8
9. Pigweed
Pigweed or tumbleweed grows around roadsides and lawns in most of the western and northern United States. It releases its pollen from spring to fall.
Pigweed, popularly known as amaranth in culinary terminology, is a family of plants with a wide variety of wild and domesticated species that exist all over the Americas. All its parts are edible and are used in various cuisines.
It is thought to have originated in the Americas and then spread to Europe, Asia, and Africa sometime after European colonization. Research on patients who had allergic rhinitis symptoms and/or signs showed that over 18% of the patients were allergic to rough pigweed pollens.9
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