Analysis: Christmas tree syndrome is a seasonal allergy triggered by trees, wreaths and garlands

By Emma Markey, TU Dublin and David O'Connor, DCU

The festive season is upon us and seasonal allergies might be the last thing on your mind while you're rocking around that Christmas tree. However, if you find yourself experiencing an increase in "hay fever" like symptoms, you could be suffering from a little-known condition called "Christmas tree syndrome".

This syndrome, as the name suggests, is a seasonal allergy triggered by your Christmas tree as well as other decorations made from plant material such as wreaths and garlands. Who knew that decking the hall with boughs of holly could be the cause of that sneezing fit?

But Christmas tree syndrome is more common than you might think and could affect up to 35% of allergy sufferers. Although you might love the smell of a real Christmas tree (Alpha pinene in case you were wondering), there might be a lot more wafting through the air.

A dramatic increase in allergy symptoms around the Christmas period has been noted for decades, although most chalk it up to colds or flus (and now we can add Covid to that list). It wasn't until the late 1960s and early 1970s that scientists really started to examine the other causes. It turns out that the noble tannenbaum can play host to a range of potential allergens that can wreak havoc on your sinuses, including pollen grains, dust mites and fungal spores.

Although allergies to certain pollen types are common, few plants produce pollen during the winter months. However, your tree could harbour pollen (pine, grass etc) collected throughout the year, re-suspending these allergy-causing particles in the confines of your lovely home.

While this is a possibility, it’s another bioaerosol that is the main culprit of Christmas tree syndrome. Fungal spores are released from moulds and other fungi. Mould can be naturally present on the Christmas tree and can be found on the trunk, bark and even on the needles. Bringing moulds inside to a nice warm setting with limited ventilation provides an ideal environment for them to grow and release spores. This release of spores in an enclosed indoor space is what leads to the swift triggering of allergies and potential dampening of your Christmas spirit.

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From RTÉ Radio 1's Morning Ireland, Karen Morton from Kilakee Christmas tree farm on demand for trees this year

In a 2011 study, over 50 different types of mould were identified in Christmas trees. The 50 types identified were dominated by four highly allergenic spore producing families of mould: Alternaria, Aspergillus, Cladosporium and Penicillium. The health effects associated with exposure to these spores is well known and can cause symptoms such as sneezing, coughing, eye/throat irritation, sinus pain, general feelings of fatigue as well as exacerbating other respiratory conditions such as asthma. If that wasn't bad enough, exposure to warm lights and central heating only makes things worse. It’s no wonder Rudolph’s nose is so red.

The negative health effects induced by fungal spore only comes into effect when the spore concentrations released into the air exceed a certain limit. Although this might not necessarily be a problem in an outdoor setting where there is a lot of ventilation, it is a completely different story when those spores are concentrated in a small indoor area. The cold winter weather often prevents us from opening windows, limiting the aeriation within our homes, meaning our festive fungal spores can reach critical levels within a number of days.

The longer the tree stays inside, the higher the spore concentrations will be and your risk of experiencing allergies will remain high. People are now putting their Christmas decorations up earlier than ever before with trees staying in most homes for the best part of a month. This only increases your chances of suffering from Christmas tree syndrome. You wouldn’t want Santa to have irritated eyes after visiting your house as he needs his sharp eyesight for his naughty and nice list.

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From RTÉ Radio 1's Ray D'Arcy Show, Colm Crowley from Christmastree.ie on their new eco-friendly Christmas tree rental service

Don’t let this news turn you into a grinch. There are several actions you can take to combat Christmas tree syndrome. The condition is only triggered by spores found in real trees so you can always try swapping to an artificial tree instead. Although if you do decide to ditch the pine for plastic, keeping it dust free is key to curbing any additional allergies (dust mites) that could pop up.

If you cannot be without your festive foliage there are some steps that can limit allergen release and help ease your seasonal sniffles. Thoroughly washing or rinsing your Christmas tree (and wreaths etc) before bringing it inside can help remove any excess spores and pollen. However, it is important not to leave it drying outside for too long as that could promote mould growth.

Alternatively, you could try putting up you Christmas tree as late as possible and keep socially distanced from your tree, in an effort to limit exposure and prevent symptoms. Finally, you could use an air filter to remove those pollen and fungal spores before they can cause any problems. Let’s hope the only surprise you get this Christmas is wrapped and under your tree and not being released by it.

Emma Markey is a PhD student at the School of Chemical and Pharmaceutical Science at TU Dublin and is a Irish Research Council Government of Ireland Postgraduate awardee. Dr. David O'Connor is an assistant professor at the School of Chemical Sciences at DCU. He leads a research group currently focussing on establishing an Irish Bioaerosol monitoring network.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ