Christmas tree allergies

Christopher Brooks, MD, an allergist at the Ohio State University Wexner Medical Center, names mold, dust, lingering pollen and a component of the sap as possible causes of reactions to a Christmas tree.¹¹ The AAAAI says an allergy to the tree itself is unlikely, but that its fragrance may be irritating and that some trees may be home to microscopic mold spores that trigger asthma or allergies.¹ Three studies add detail: a 1970 study of allergy patients and of homes with trees, a 2011 letter on mold found on tree clippings, and a 2024 study of what one freshly cut tree gave off in a test chamber.⁸¹⁰¹²

What people notice around the tree

Brooks writes that Christmas trees can cause an allergic reaction in some people, with watery eyes, runny noses or trouble breathing.¹¹ He notes that it is sometimes called Christmas tree syndrome, or Christmas tree dermatitis when the reaction is a rash.¹¹

In a study published in the Canadian Medical Association Journal in December 1970, Derek Wyse and David Malloch reported that respiratory and skin allergies to conifers occurred in 7% of 1,657 allergic patients.⁸ They described the seasonal syndrome as including sneezing, wheezing and short-lived skin rashes.⁸ Most of the patients developed symptoms within 24 hours, but 15% had symptoms after a delay of several days.⁸

Mold on live trees

ACAAI says some live trees still have mold spores and pollen on them, which can cause nasal allergies to flare.⁴ Brooks writes that mold growing on the tree is most likely what triggers the reaction.¹¹

In the 1970 study, scrapings from pine and spruce bark yielded large numbers of Penicillium, Epicoccum and Alternaria, but these molds failed to become airborne.⁸ At 10 test sites sampled before, during and after a tree was placed in the home, the authors found no significant change in airborne fungi while trees were present.⁸

The 2011 report was a letter by Lawrence Kurlandsky and three colleagues, “Identification of mold on seasonal indoor coniferous trees,” in the June 2011 issue of the Annals of Allergy, Asthma & Immunology, and its PubMed record has no abstract.⁹ A SUNY Upstate Medical University news story about it says faculty and staff from Upstate’s pediatrics, microbiology and pathology departments provided clippings of their own Christmas trees, and that 53 different types of mold were found among the 28 samples.¹⁰ The story says many were molds not known to trigger allergies, but that the four most prevalent are known allergens.¹⁰ It describes tests on the clippings only and reports no sampling of indoor air and no check of anyone’s symptoms.¹⁰

Our Aspergillus and Cladosporium pages cover two other molds, and the mold spore counts guide explains how spores in the air are counted.

Pollen in December

ACAAI says pine pollen is produced when the trees reproduce in the springtime.³ An allergist it quotes, Allen Meadows, MD, says pine tree allergies and Christmas tree allergies are separate things, and that by Christmas time the tree pollens are all gone.³ He says the things on Christmas trees that bother people are different types of pollen, adding that the weed pollens come in the fall.³

The USDA Forest Service’s silvics manual says Fraser fir flower buds usually open from mid-May to early June, and it calls the tree unequaled as a Christmas tree.¹³ Balsam fir flower buds usually open in late May or early June, and the manual, published in 1990, placed balsam fir among the top three Christmas tree species.¹⁴

Pollen can still ride in on a tree: AAFA says live pine trees can bring mold and pollen into a home.⁶ In the 1970 study, pollen sampling showed weed, grass and tree pollens released into the air while Christmas trees were in the house, and the abstract does not say where that pollen came from.⁸ Brooks writes that dust on the branches and some lingering pollen from the pine or other plants could contribute, to a lesser extent.¹¹

Outdoors, one pollen season does begin in December: the Texas A&M Forest Service says mountain cedar trees in Texas typically begin producing pollen in mid-December and peak in mid-January.¹⁵ Our cedar fever guide covers that season.

Sap, scent and skin

Writing about fresh fir trees and wreaths, ACAAI says some people have contact skin allergies to a substance called terpene, found in the sap of trees.⁴ Brooks writes that people with rashes might be allergic to a component of the tree’s sap.¹¹ Our contact dermatitis page covers rashes where something touched the skin. The 1970 authors wrote that oleoresins of the tree balsam are thought to be the most likely cause of the symptoms they called Christmas tree allergy.⁸

A 2024 study by National Institute of Standards and Technology scientists, published in the journal Indoor Environments, measured the volatile organic compounds one freshly cut Douglas fir gave off over 17 days in an environmental chamber.¹² Its monoterpene emissions were 12.4 milligrams an hour on the first day and fell to 1 milligram an hour by day three.¹² Over the first two to three days, the authors write, the tree released amounts of monoterpenes comparable to personal care products, air fresheners or other household goods.¹² Assuming a significant portion of the signal was limonene, they write, the concentrations were in the range of limonene’s odor thresholds but far below sensory irritation or workplace limitation values.¹² They note that the workplace limit they cite is set for healthy working adults and does not consider vulnerable groups such as pregnant women, young children and elderly people.¹² The paper does not discuss allergy or asthma, and its authors call the experiment exploratory and say a sample size of one tree is not holistic.¹²

Artificial trees and stored decorations

AAFA says artificial trees and decorations stored in a garage or basement can have mold and dust on them, and that cardboard boxes and open bags allow dust to accumulate.⁶ Its holiday advice mentions storage containers that keep out dust mites.⁶ ACAAI likewise says decorations stored in attics, basements or garages often collect dust, mold spores and other allergens.⁵ Brooks writes that a fake tree might not be any better if it is dusty or stored in a damp basement, humid garage or attic where mold can grow.¹¹

The AAAAI says inhaling artificial snow or flocking sprays can irritate the lungs and trigger asthma symptoms.¹

Wreaths and poinsettias

AAFA says real live trees and wreaths can have pollen and mold spores all over them.⁷

David Trinklein, a University of Missouri Extension horticulturist, notes that poinsettia sap, which has several proteins in common with natural latex rubber, can cause allergic skin reactions.¹⁶ University of Illinois Extension says the foliage and stem contain a milky sap that may irritate the skin, especially for people with a latex allergy.¹⁷ It adds that in a worst case scenario there is potential for allergic reactions in some, though the overwhelming evidence shows little risk in bringing the plants home.¹⁷

What the sources leave open

None of these sources gives a figure for how common these reactions are in the general public: the AAAAI says only that some individuals can be allergic to Christmas trees, and the 7% figure from 1970 came from people who were already allergy patients.²⁸ The sources also differ on the main cause: Brooks points to mold, the allergist quoted by ACAAI to different types of pollen, and the 1970 authors to the tree’s oleoresins.¹¹³⁸ The one study here that sampled air in homes with trees found no significant change in airborne fungi, and Upstate’s account of the 2011 letter describes mold tests on clippings, not air sampling.⁸¹⁰

The groups’ own suggestions differ in detail. The AAAAI’s winter holidays page suggests letting a real tree dry in a garage or enclosed porch for a week and shaking it before bringing it inside, and its holidays page suggests a thorough shake and a few days of drying in a covered area.¹² ACAAI suggests a thorough shake and rinse.⁵ For questions about reactions to a tree or other holiday greenery, talk to an allergist.