Why Christmas Trees Smell So Good

Chemistry of the Christmas Tree Aroma

A Christmas tree gets its special smell from terpenes, which vary depending on the type of tree. Plastic trees smell mostly of flame retardant chemicals.
A Christmas tree gets its special smell from terpenes, which vary depending on the type of tree. Plastic trees smell mostly of flame retardant chemicals. Image by J. Parsons, Getty Images

Is there anything more wonderful than the smell of a Christmas tree? Of course, I'm talking about a real Christmas tree rather than an artificial tree. The fake tree may have an odor, but it's not coming from a healthy mix of chemicals. Artificial trees release residues from flame retardants and plasticizers. Contrast this with the aroma of a freshly cut tree, which may not be all that healthy either, but certainly smells nice.

Curious about the chemical composition of Christmas tree aroma? Here are some of the key molecules responsible for the smell:

α-Pinene and β-Pinene

Pinene (C10H16) occurs in two enantiomers, which are molecules that are mirror images of each other. Pinene belongs to a class of hydrocarbons known as terpenes. Terpenes are released by all trees, although conifers are particularly rich in pinene. β-pinene has a fresh, woody fragrance, while α-pinene smells a bit more like turpentine. Both forms of the molecule are flammable, which is part of why Christmas trees are incredibly easy to burn. These molecules are volatile liquids at room temperature, releasing most of the characteristic Christmas tree smell.

An interesting side note about pinene and other terpenes is that plants partially control their environment using these chemicals. The compounds react with air to produce aerosols that act as nucleation points or 'seeds' for water, promoting cloud formation and conferring a cooling effect.

The aerosols are visible. Have you ever wondered why the Smoky Mountains actually appear smoky? It's from the living trees, not campfires!

Bornyl Acetate

Bornyl acetate (C12H20O2) is sometimes called "heart of pine" because it produces a rich odor, described as balsamic or camphorous. The compound is an ester found in pine and fir trees.

Balsam firs and silver pines are two types of fragrant species rich in bornyl acetate that are often used for Christmas trees.

Other Chemicals in "Christmas Tree Smell"

The cocktail of chemicals that produces "Christmas tree smell" depends on the species of tree, but many conifers used for Christmas trees also waft odors from limonene (a citrus scent), myrcene (a terpene partly responsible for the aroma of hops, thyme, and cannabis), camphene (a camphor smell), and α-phellandrene (peppermint and citrus-smelling monoterpene).

Why Doesn't My Christmas Tree Smell?

Just having a real tree doesn't guarantee your Christmas tree will smell Christmas-y! The fragrance of the tree depends primarily on two factors.

The first is the health and hydration level of the tree. If the tree isn't taking up water, it's sap won't be moving, so very little scent will be released. Ambient temperature matters, too, so a tree outdoors in the cold won't be as fragrant as one at room temperature.

The second factor is the species of tree. Different types of tree produce different scents, plus some kinds of tree retain their fragrance after being cut better than others. Pine, cedar, and hemlock all retain a strong, pleasing smell after they have been cut.

A fir or spruce tree may not have as strong a smell or may lose its scent more quickly. In fact, some people strongly dislike the odor of spruce. Others are downright allergic to the oils from cedar trees. If you're able to select the species of your Christmas tree and the smell of the tree is important, you might want to review tree descriptions by the National Christmas Tree Association, which includes characteristics such as odor.

If you have a living (potted) Christmas tree, it won't produce a strong smell. Less odor is released because the tree has an undamaged trunk and branches. You can spritz the room with Christmas tree fragrance if you want to add that special aroma to your holiday celebration.