O Christmas tree: Why are your needles so … aromatic?

What comes to mind when you think about Christmas? Snow, gingerbread, gift-giving?

What about methyl salicylate? If you were thinking about the smell of Christmas trees, then you’ve got a match! Although it sounds like something Walter White might have used in his dubious operations on Breaking Bad, methyl salicylate is the pungent chemical mostly responsible for that fresh piney scent that comes from your Christmas tree.

Methyl salicylate is a type of chemical called an ester. Made up mostly of carbon, hydrogen, and oxygen atoms, some of these compounds are known for their smelly characteristics.

In fact, many of our favourite fruits — oranges, apples, pears, and bananas — get their distinctive aromas from the cocktail of esters produced and released by the fruit. Methyl salicylate happens to be the ester of choice for wintergreen plants, like pine, spruce, and fir trees.

Why do trees and other plants produce esters? Well, just like the smell of smoke warns us about fire, some plants use odours as a signal to other plants and animals about something that is happening nearby.

Scientists have found that some plants may start producing methyl salicylate after they have been infected by a virus, so the scent of the methyl salicylate acts as a pheromone, or signal, to nearby plants that they should start putting up their antiviral defences in order to stay healthy.

Other studies have shown that insects that eat other insects are attracted to the smell of methyl salicylate, which can help a plant fight off insects that are trying to eat it.

But we aren’t trees that are worried about herbivorous insects eating us, so why do humans enjoy the smell of methyl salicylate? A study done in Japan found people who walked through wintergreen forests were less likely to feel hostile or depressed, and people who had higher stress levels had greater feelings of relaxation after their forest walk.

Memory is also a big factor in why we humans enjoy the smell of methyl salicylate. All those happy memories of Christmas holidays are wrapped up in the smell of wintergreen trees, which your brain associates with positive feelings.

So, if your least favourite part of the holidays is having to clean up after your Christmas tree, this year it may just be time to give Walter White a call to see if he can supply you with some methyl salicylate to put in a corner. It might not look like Christmas but your nose will know it is – and your vacuum cleaner will thank you.

Jenna Friedt is a science communication student at Laurentian University.