Why do Christmas trees smell so good, and why has mine stopped?
4 min read · Published
The chemistry behind the smell of a real Christmas tree, which trees smell strongest, and why the scent fades after the first few days.
The smell comes from a sticky resin in the tree called oleoresin. Conifers make it to defend themselves against insects and disease. Indoors, the warmth of the room makes chemicals in the resin, called terpenes, evaporate into the air. Those are what you smell (NC State University).
In a 2004 survey of the UK’s favourite smells, real Christmas trees came eighth, just behind the sea and ahead of perfume (BCTGA).
What you are smelling
Conifers contain several hundred terpenes. Justin Whitehill, who runs the Christmas Tree Genetics Program at NC State University, picks out the main ones (NC State University):
| Compound | Smells like |
|---|---|
| Pinene | Fresh pine woods, the classic Christmas smell |
| Limonene | Citrus |
| Myrcene | Thyme |
| Camphene | Camphor |
| Phellandrene | Mint |
| Bornyl acetate (not a terpene) | Woody, balsamic |
Each species has its own mix, and individual trees differ too. Whitehill says trees are “sort of like humans in that they’re different from each other at the individual level”. Two Nordmann firs from the same field can smell slightly different.
Which trees smell strongest
Of the trees sold in the UK, the RHS describes Norway spruce as having “a good scent” and Fraser fir “a lovely pine fragrance” (RHS). NC State calls Fraser fir’s scent “one of the most appealing aromas to consumers” (NC State University).
The Nordmann fir, the UK’s best seller, is milder. That matches what many UK buyers say (Reddit r/CasualUK). Scent and needle retention are different characteristics to consider. If scent matters more than tidiness, a Norway spruce is the traditional choice. See Nordmann fir or Norway spruce.
Researchers at Washington State University are studying which scent compounds make people prefer one tree over another (WSU).
Why the smell fades
The smell is strongest on the first day and drops quickly. In 2023, scientists at NIST sealed a Douglas fir in a test chamber for 17 days and measured what it released. They found 52 different scent compounds (monoterpenes). Levels peaked on the first day. By the third day they had fallen to about a tenth of the starting level (NIST).
So if your tree smelled wonderful when it arrived and you can barely smell it a few days later, that matches what NIST measured. It doesn’t by itself mean the tree is drying out. Check the needles and the water level to be sure. See Why is my Christmas tree dropping needles?
How to get more smell from your tree
- Choose a species with more scent, such as Norway spruce or Fraser fir.
- Keep the room comfortably warm, but don’t overheat the tree. NC State explains that warmth is what makes the terpenes evaporate. But the RHS warns that a tree too close to a radiator or fire loses moisture and drops needles (RHS).
- Use the trimmings. If you cut off the lowest branches to fit the stand, put them in a vase of water away from fires, candles and other heat sources.
If the smell bothers you
Some people get watery eyes or a runny nose from the scent compounds. NIST suggests opening a window near the tree, or leaving a newly cut tree in a garage or outside for three days before bringing it in, while the emissions die down (NIST). Dustin Poppendieck, who led the study, said “for most people, this shouldn’t be a major concern. I’m still going to have a Christmas tree in my house.” For sneezing and allergies, see Can you be allergic to a Christmas tree?