AcOpal gemstonetually, the gemstones called opals don’t have anything to do with allergies, but OPALS® does.  This acronym stands for Ogren Plant-Allergy Scale, a tool to help individuals make smarter, more informed decisions about plant selections for use in and near their homes, in cities, in parks, and around hospitals and schools.

OPALS® has been used not only by individuals and organizations, but by various state departments of public health and by the U.S. Department of Agriculture in landscape planning designed to reduce exposure to allergens by humans.

What is OPALS?

OPALS® is the world’s first plant-allergy scale, an effort to measure the allergy potential of garden and landscape plants.  The scale is a numerical one with numbers ranging from 1-10.  Plants given a 1 or 2 are considered to have low allergy potential and affect few, if any people, while those assigned a 10 are considered to have high allergy potential and affect a large number of people.  The table at the end of this blog gives the scale and guidelines for what a particular number on the OPALS scale means.                                                                                       Allergy Free Gardening

The OPALS allergy scale was first published in 2000 in a book written by T. L. Ogren titled, “Allergy-Free Gardening.”  The scale covers over 3000 different plants that are commonly planted in gardens and landscapes, and which are likely present in an urban environment.  Each plant is assigned a number based upon more than 130 criteria.

A factor may be positive or negative, and not all factors are weighted equally since some are of greater importance than others in determining a plant’s potential for being an important producer of allergens.  For example, pollen allergies caused by inhaling pollen that leads to allergic rhinitis and asthma, are given greater weight than odor allergies.

Plant Allergy Ranking Factors

Some of the factors used to rank a plant are:
· The amount of pollen produced, if any
· Potency of the individual pollen grains
· The amount of time during a year that the plant is in bloom
· The size, density, shape, and weight of the pollen grains
· The dryness or stickiness of the grains
· Is the tree perfect flowered, monoecious, dioecious, or polygamous?
· Sex of plant, if dioecious
· Position on the plant of pollen flowers
· Average rankings in actual skin scratch, patch, and sniff tests
· Cross-reactivity to food allergies”
(from Safe Gardening)

(Definitions: perfect flower – bisexual; having male and female reproductive structures present in the same flower; monoecious – flowers imperfect or unisexual, male and female flowers are separate but on the same plant; dioecious – flowers imperfect, male and female flowers are borne on different plants; polygamous – imperfect and perfect flowers borne on same plant.)

What Can You Do to Reduce Allergies in Your Neighborhood?

Homeowners desiring to reduce the amount of allergy-triggering pollen in their neighborhood should plant female trees rather than male trees, and use those species of trees and landscape plants that have low allergenicity.  Urban neighborhoods should work with city officials when plantings are being considered for use in parks and along streets to ensure that trees and shrubs that are used have a minimal impact on the level of allergy triggering pollens released into the air.

OPALs is a convenient method to address the question of how allergenic potential plants might be in an area, and what might be alternatives to provide the shade, beauty, and/or food for wildlife that is desirable, while avoiding undesirable levels of allergens.

OPALS Scale Guideline*
1-3: Very low potential to cause allergies
4-6: Moderate potential to cause allergies, exacerbated by over-use of the same plant throughout a garden
7-8: High potential to cause allergies, advise to plant as little as possible
9-10: Extremely high potential to cause allergies, should be replaced with less allergenic species
*Ogren, Thomas Leo (2000). Allergy-Free Gardening. Berkeley, California: Ten Speed Press.

Examples of the use of the above table for landscaping purposes:
Male mulberry trees have a ranking of 10 and should be replaced with female mulberry trees or with a different species of tree altogether.

A variety of red maple such as ‘Autumn Glory’ produces no pollen and is given a ranking of 1.  Depending on the desired use of the tree for landscaping, this maple variety would be an excellent choice because of its low impact as an allergen source.

Visit Ogren’s website, if you would like to read more about OPALS and Allergy Free Gardening.

H. Wayne Shew, Ph.D.
NAB certified counter
BSC/AAAC Collection Station—Birmingham, Alabama

Note: This blog is not intended to be an endorsement of the use of OPALS, either by me or by Alabama Allergy & Asthma Center, as a means of reducing your personal allergies.   It is written to provide information on a topic that you may have heard or read about at some time in the past, or that you might have an interest in learning more about in the future.