OPALS (Ogren Plant Allergy Scale)
The OPALS allergy scale was first published in "Allergy-Free Gardening", by Thomas Leo Ogren, in 2000. It covers over 3,000 common trees, shrubs, flowers, and grasses. The allergy scale was updated and extended in 2015 in "The Allergy-Fighting Garden".
The Ogren Plant Allergy Scale takes into account pollen allergies, contact allergies, and odor allergies, with higher weighting given to pollen allergies that are caused by inhaling pollen into the lungs. Additionally, plants that cause contact allergies (such as rashes or itching), or that are highly poisonous when ingested even though their pollen does not cause respiratory allergies, are never given low ratings.
Low allergy ratings are considered to be 1 through 3 on the allergy scale. Mid-range ratings are 4 through 6, and high ratings are 7 through 10. Plants with ratings of 9 or 10 have an extremely high potential to cause allergic reactions.
|1–3||Very low potential to cause allergic reactions|
|4–6||Moderate potential to cause allergic reactions, exacerbated by over-use of the same plant throughout a garden|
|7–8||High potential to cause allergic reactions, advise to plant as little as possible|
|9–10||Extremely high potential to cause allergic reactions, should be replaced with less allergenic species|
Within the United States: OPALS has been adopted for use by the American Lung Association and the U.S. Department of Agriculture Urban and Community Forest Service. More recently, the California Public Health Department has endorsed the use of this allergy scale in city landscape planning to reduce asthma.
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