OPALS (Ogren Plant Allergy Scale)

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OPALS is an acronym for Ogren Plant Allergy Scale.[1] It is an allergy rating system for plants that measures the potential of a plant to cause allergic reactions in humans.

Scale System[edit]

The OPALS allergy scale was first published in "Allergy-Free Gardening", by Thomas Leo Ogren, in 2000.[1] It covers over 3,000 common trees, shrubs, flowers, and grasses.[2] The allergy scale was updated and extended in 2015 in "The Allergy-Fighting Garden".[3][4][5]

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.[1]

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.

OPALS Rating Guideline[1]
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.[1] More recently, the California Public Health Department has endorsed the use of this allergy scale in city landscape planning to reduce asthma.[6][7]

Within Canada: The OPALS allergy scale was used in the Canadian Urban Allergy Audit, which was conducted in 2012.[8][9]

Within the United Kingdom: OPALS allergy scale labels for plants sold at nurseries have recently become available for use within the United Kingdom.[10][11]


  1. ^ a b c d e Ogren, Thomas Leo (2000). Allergy-Free Gardening. Berkeley, California: Ten Speed Press. ISBN 1580081665.
  2. ^ Harrar, Sari N. "Sick of Sneezing? Allergy-Proof Your Yard". Retrieved 3 May 2014.
  3. ^ Zacharias, Colleen. "Sneeze, wheeze... solutions, please". Retrieved 5 May 2014.
  4. ^ "Tom Ogren". calpoly.academia.edu. Retrieved 5 May 2014.
  5. ^ Ogren, Thomas (2015). The Allergy-Fighting Garden. Berkeley, CA: Ten Speed Press. ISBN 9781607744917.
  6. ^ Ogren, Thomas. "A Plan for Cities Wishing to Reduce Pollen-Allergies and Related Allergic-Asthma". icangarden.com. Retrieved 3 May 2014.
  7. ^ "Strategic Plan for Asthma in California" (PDF). cdph.ca.gov. Retrieved 12 May 2018.
  8. ^ "Canadian Urban Allergy Audit" (PDF). Marketwire.com. Retrieved 3 May 2014.
  9. ^ McCusker, Kris. "Urban allergy audit provides glimmer of hope for Toronto allergy sufferers". 680news.com. Retrieved 3 May 2014.
  10. ^ "OPALS". Society for Allergy-Friendly Environmental Gardening. Retrieved 17 January 2016.
  11. ^ Hansen, Jolene. "Put Pollen in its Place". Garden Center. Retrieved 25 June 2016.

External links[edit]