That Christmas tree smell is the scent of coniferous evolution. Over millions of years, these trees have equipped themselves with a cocktail of chemical weaponry, including substances that act as fungicides and bactericides, and those that deter herbivorous pests, large and small. The chemical combination varies between tree species, but generally consists of a mix of aromatics, including terpenes such as alpha and beta-pinene, limonene and camphene, and also esters such as bornyl acetate. By happy coincidence, we tend to find these combined scents appealing - so much so that they are added to perfumes and commercial air fresheners.
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