During the winter months, the festive season of Christmas is celebrated by many around the world, but are the traditions of Christmas causing more problems than joy for some? From unwrapping gifts under the Christmas tree to the choice of decorations around homes, schools and offices, our Christmas traditions can increase allergen exposure, posing a risk to those with respiratory allergies. But even those who choose not to celebrate Christmas are at risk of an increase in winter allergies, as the colder months bring conditions for mould to thrive, dust to gather, and indoor pet dander to increase; questioning are winter allergies being overlooked? Seasonal allergic rhinitis is often thought to be associated with the warmer months, but this may be a misconception, as winter (December–February) has in fact been shown to have the highest peak in allergic rhinitis cases (Chen et al., 2012). Despite this, winter allergies are still considered rare and often misdiagnosed.
The Christmas tree is often the centre of the festive celebrations, and the decision of whether to buy a real or artificial tree is debated in households annually. While both options have their pros and cons for decorative purposes, it may be surprising that both options also bring unwanted allergens into the home.
Allergy to Christmas trees hasn’t been widely reported in medical journals and is considered relatively rare; a retrospective analysis of 1,561 patient records identifying self-reported seasonal exacerbation of respiratory allergies, found only 21 patients (1.66%) experienced allergies during the Christmas period (Wyse & Malloch, 1970). After conducting the initial phase of their study, Wyse & Malloch investigated the issue further, carrying out a prospective study, including 1,657 patients with respiratory allergies and urticaria. Patients were asked if they experienced a seasonal flare-up of allergic symptoms with the introduction of a Christmas tree into the home and the time of onset in relation to interaction with the tree. A total of 94 patients reported seasonal allergic symptoms in relation to the tree, a surprisingly high number, equating to 7.6% after excluding those without a real tree in the home. Among patients experiencing Christmas allergies, chronic allergic rhinitis was the most common allergic disease, and sneezing was the most common symptom evoked by the tree (figure 1).
However, the exact cause of these allergic reactions can vary due to the number of allergens linked to Christmas trees. In Wyse & Malloch’s study, the majority of respiratory allergic symptoms were experienced while decorating or trimming the tree or within 24 hours, suggesting these patients were sensitised to the balsam of the tree. However, 15% of patients reported that their reaction began three or four days after the tree was set up, and some symptoms worsened over time as the tree dried (Wyse & Malloch, 1970).
Christmas trees are often kept in a damp environment before purchasing which encourages mould spores to thrive. Mould is a common cause of allergic rhinitis and is particularly prevalent in the autumn and winter months. For the final phase of Wyse & Malloch’s study a particle analysis was carried out in 8 homes before, during, and after a Christmas tree was introduced, with the tree being in the home for five days. The results revealed a dramatic increase in mould colonies after the introduction of the tree. Interestingly, after removing the tree mould colonies decreased but didn’t return to baseline levels (table 1).
Despite the increase in mould colonies seen the results of the mould analysis remained inconclusive as the colonies collected didn’t match those collected from pine-tree scrapings, suggesting the mould had come from another source. Pollen, on the other hand, provided a more reliable indication of the cause of Christmas tree allergies. Ragweed and grass pollen appeared in all of the homes after the introduction of the Christmas tree. An increase in pollen presence was recorded immediately after the introduction of the tree into the home, and then a second peak was seen a few days later when the trees had begun to dry. Wyse & Malloch theorised that pollen grains become adherent to the sticky branches and needles of the tree during the summer and autumn months and are released into home as the branches dry (Wyse & Malloch, 1970).
While many with mould allergies may, therefore, opt for an artificial tree, they may not manage to avoid allergen exposure entirely. As artificial trees and decorations are often stored in dark and damp areas of the home during the year, they are also prone to collecting mould and dust, triggering rhinitis symptoms. Air sampling from homes with artificial trees initially showed low levels of mould spores when the tree was introduced, but the dismantling of the tree released higher mould spore, pine, and ragweed pollen levels (Alexander et al., 2006; Medpage Today, 2006).
Other plants have also been linked to winter allergies, including the decorative poinsettia plant (Euphorbia pulcherrima [Ep]). The so-called “Christmas flower” is a rubber plant and has been linked with cases of contact dermatitis in patients with latex allergies. However, one case of a six-year-old boy who had experienced allergic rhinitis and asthma symptoms on two consecutive winter seasons reported the child was sensitised to the Ep allergen and grass on a skin prick test (Ibáñez et al., 2004).
It may seem as if bringing plants indoors is the culprit of this increase in winter allergies, but for some, outdoor allergens are unavoidable. One study in Switzerland reported an increase in allergic rhinitis symptoms during the winter months in school children. The increase came after alder trees were planted along the main route into the school, leading to almost daily exposure to alder pollen during December when the trees are flowering. The study measured IgE antibodies to 103 molecular allergens in 54 students in 1986 (before the introduction of the alder trees) and retested 12 of the former students again in 2010. Interestingly, retesting revealed 25% of former students had newly detectable IgE antibodies to alder pollen.
Another group of 46 students were recruited in 2006 shortly after the trees were planted, with 6 reporting allergic symptoms during the winter. Because winter allergies are considered uncommon, the rhinoconjunctivitis symptoms the children were experiencing were often thought to be attributed to the common cold. However, when these 6 children were tested, they were all sensitised to alder pollen (Gassner et al., 2013).
Could a runny nose be more serious than it seems? Misdiagnosis and undiagnosed allergic rhinitis remain common problems for patients with respiratory symptoms, and clinical judgement could be skewed during the winter months with the rise in cold-like symptoms. It is important to consider if environmental factors, like Christmas trees, could be the root cause of these winter respiratory symptoms. To find out more about allergic rhinitis diagnosis and how to manage these common respiratory symptoms and comorbidities over the upcoming festive period visit the disease awareness section of the allergic rhinitis knowledge centre.
Alexander M, Plumley M, Anderson J, Alexander J. Yuletide Allergy Symptoms. Presented at the American College of Allergy, Asthma & Immunology meeting 2006, 09–15 November 2006. Philadelphia, United States of America. P200.
Chen BY, Chan CC, Han YY, Wu HP, Guo YL. The risk factors and quality of life in children with allergic rhinitis in relation to seasonal attack patterns. Paediatr Perinat Epidemiol. 2012;26:146–55.
Gassner M, Gehrig R, Schmid-Grendelmeier P. Hay fever as a Christmas gift. N Engl J Med. 2013;368:393–4.
Ibáñez MD, Fernández-Nieto M, Martínez J, Cardona GA, Guisantes J, Quirce S, et al. Asthma induced by latex from 'Christmas flower' (Euphorbia pulcherrima). Allergy. 2004;59:1127–8.
Medpage Today, 2006. Available at https://www.medpagetoday.com/meetingcoverage/acaai/4483 (accessed December 2018).Wyse DM, Malloch D. Christmas tree allergy: mould and pollen studies. Can Med Assoc J. 1970;103:1272–6.
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