By A Reis
Having ornamental plants is a popular choice to add colour and variety to your house or work place, but for some people just being in close proximity to plants is enough to trigger an allergic reaction.
Unfortunately, this is an area poorly researched and, in many cases, the actual allergen has not been identified yet. Most studies concentrate on occupational allergy, such as in gardeners, greenhouse workers and florists, but with the widespread use of plants in many public places, the exposure to allergens reaches many more.
Do plants prevent or cause allergies?
The answer may be both, depending on the allergy.
In addition to their decorative aspect, in 1989 NASA published a study that demonstrated that plants are capable of a much more important function than just their ornamental status. Certain plants can eliminate toxins present in the air, which make them exceptional air cleaners providing a much better atmosphere inside the house.
It was shown that plants absorb these substances through the leaves, as well as releasing moisture which reduces airborne toxins. This included pet dander and dust mites, as well as many other allergens. The study suggested the use of such plants as an inexpensive means of providing clean air indoors, particularly public places.
If you suffer from allergies, after reading this report, you would think that having plants in your house can potentially reduce the incidence of allergens and eliminate any symptoms. This is not the full story however, as many plants operate at the other end of the scale by triggering an allergic reaction, making life very difficult for those that have to cope with this condition.
If you start experiencing certain symptoms connected with your allergy suddenly after acquiring a new plant, unfortunately it may mean a plant allergen is the culprit.
There are hundreds of different plant allergens that can cause a reaction, either by contact or inhalation. It is estimated that over 500 substances can cause such reaction from one plant family alone. These allergens vary immensely in their composition and diagnosis is sometimes difficult due to lack of tests specific for each one. In addition, exposure to more than one allergen simultaneously further complicates diagnosis.
Traditionally, classification of allergens is done based on botanical criteria of the correspondent plant, but this does not allow doctors to predict cross-reactivity to advise patients about what other plants have the same allergen and therefore should be avoided. Recently however, a classification based on the allergen’s chemical structure has been proposed which, if accepted, would facilitate finding identical allergens present in different plants but likely to cause the same reaction.
Most common plants allergens
According to scientific research and medical cases, ornamental plants most likely to trigger an allergic reaction include:
• Chrysanthenum (Compositae family)
• Tulips, hyacinths, lilies, crocuses (Liliaceae family)
• Roses (Rosaceae family)
• Weeping fig (Moraceae family)
• Primulas (Primulaceae family)
• Stephanotis floribunda (Apocynaceae family)
• Spider plant and snake plant (Asparagaceae family)
• Cymbidium and oncidium orchids (Orchydaceae family)
• Marigold, dahlia and sneezeweed (Asteraceae family)
• Tradescantia (Commelinaceae family)
• Ginkgo (Ginkgoaceae family)
• Silk oak (Proteaceae family)
What are the symptoms caused by plant allergens?
Obviously, symptoms depend on the way you get into contact with the allergen. You can either enter in direct contact with the allergen by touching the plant, which will cause various skin conditions; or indirectly, by inhaling airborne allergens, which will cause respiratory problems.
Direct contact with allergen causes skin reactions
Some plants secrete liquid from the fruit, leaves and stem, which can be potentially trigger an allergic reaction. If you touch the offending plants, your skin gets in contact with these substances and may cause itching, eczema, skin lesions, contact dermatitis, urticaria or even photodermatosis. In extreme cases, it may even result in swelling in the face, usually around the eyes or mouth (angiooedema) or anaphylatic shock.
Examples of plants that can cause a skin reaction include chrysanthemum, orchids, marigold and weeping ficus.
Indirect contact with allergen causes respiratory reactions
Plants can cause allergic reactions by other means other than just by contact. Inhaling airborne allergens can result in runny nose and itchy eyes (rhinoconjuntivitis) and allergic rhinitis, as well as lung inflammation, dyspneia or even asthma.
This type of allergy can be difficult to diagnose, as contact is not necessary and it may take some time for enough allergens to accumulate in the air to cause a reaction. Potentially, any ornamental plants that produce large amounts of pollen can cause an allergic reaction, but pollen is not the only airborne allergen.
How to avoid or reduce plant allergies?
• Chose plants with flowers with little pollen and short stamens
• Keep plants at floor level, to reduce area contaminated with potential allergens
• Add one plant at a time to your house, to ensure that no allergies develop
• Chose plants with smooth leaves, as fuzzy leaves can trap allergens easily
• Examples of low allergy plants include cactus, begonia, nasturtium, peperomia and croton
• Ensure your plants are always clear of any dust which can harbour airborne allergens
• Spray the leaves with water to reduce the risk of airborne allergens
In conclusion, mostly due to lack of adequate testing, allergies caused by common house plants tend to be misdiagnosed and misunderstood. However, this can cause from mild skin irritation to serious allergic conditions that require medical attention. Further research is required to identify the chemical nature and mechanism of action of many still unknown allergens, which will help in developing new tests to facilitate diagnosis. Furthermore, a better understanding of allergens and their chemical structure would permit doctors to advise their patients about what other plants to avoid to reduce the incidence of allergic reactions.