Ogren Plant Allergy Scale

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Ogren Plant Allergy Scale
Purposemeasures plant potential to cause allergic reaction

The Ogren Plant Allergy Scale (OPALS)[1] is an allergy rating system for plants that measures the potential of a plant to cause allergic reactions in humans.[2]

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.[3] The allergy scale was updated and extended in 2015 in The Allergy-Fighting Garden.[4][5][6]

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][7]
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


  • Canada: The OPALS allergy scale was used in the Canadian Urban Allergy Audit, which was conducted in 2012.[8][9]
  • United Kingdom: OPALS allergy scale labels for plants sold at nurseries have recently become available for use within the United Kingdom.[10]


  1. ^ a b c d e Ogren, Thomas Leo (2000). Allergy-Free Gardening. Berkeley: Ten Speed Press. ISBN 1580081665.
  2. ^ Hirschlag, Ally (16 May 2020). "How urban planners' preference for male trees has made your hay fever worse". The Guardian. Retrieved 17 May 2020.
  3. ^ Harrar, Sari N. "Sick of Sneezing? Allergy-Proof Your Yard". ABC News. Retrieved 3 May 2014.
  4. ^ Zacharias, Colleen. "Sneeze, wheeze... solutions, please". Winnipeg Free Press. Retrieved 5 May 2014.
  5. ^ "Tom Ogren". Academia. Retrieved 5 May 2014.
  6. ^ Ogren, Thomas Leo (2015). The Allergy-Fighting Garden. Berkeley: Ten Speed Press. ISBN 9781607744917.
  7. ^ Prakke, Peter (2018). Veterans Gardening Guide. Tellwell Talent. p. 19. ISBN 978-1-77370-342-8.
  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. ^ Hansen, Jolene. "Put Pollen in its Place". Garden Center. Retrieved 25 June 2016.
  11. ^ Ogren, Thomas. "A Plan for Cities Wishing to Reduce Pollen-Allergies and Related Allergic-Asthma". icangarden.com. Retrieved 3 May 2014.
  12. ^ "Strategic Plan for Asthma in California" (PDF). cdph.ca.gov. Retrieved 12 May 2018.

External links[edit]