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Why Can Lavender Be Used to Repel Moths? – The Chemistry of Lavender

By: , Posted on: August 12, 2017

Hanging in the wardrobes of our flat, alongside our clothes, are a couple of small bags of dried lavender. Like many others, we keep them there to ward off clothes moths, but while offhandedly discussing this a couple of weeks ago I realised that I had absolutely no idea if there was scientific evidence to back up this repellent effect. So, I did what any good scientist would, and started a quest to find out whether lavender’s anti-moth powers were the real deal, or as scientifically holey as the moth-eaten clothes it claims to ward against!

I commenced my quest with a look into the compounds that give lavender its aroma. This seemed a fairly logical place to start – perhaps one of these compounds was the reason moths avoid dried lavender? The key constituents of lavender’s aroma are linalool and a closely related compound, linalyl acetate. Linalool is actually a widely used compound in fragrances and pops up in a lot of personal care products, but the only mention of any repellent effect I could find is on mosquitos, not moths. Other aroma compounds such as the appropriately named lavandulol and lavandulyl acetate also drew blanks when it came to any moth repellent activity.

Of course, these are not the only compounds that make up lavender aroma – over 300 compounds have been detected in lavender’s essential oil. Though not all of these will contribute to the aroma, it does not necessarily mean that minor contributors, or even compounds that do not contribute at all, might not be behind the moth repelling effect. As it turned out, this was indeed the case.

Both the compounds mentioned previously and a number of other aroma compounds present in lavender are members of the terpene family. Two such compounds found in lavender, 1,8-cineole and camphor, appear to be key contributors to the plant’s ability to keep moths at bay. A number of other terpenes have insecticidal powers too, from alpha-pinene found in conifers to camphene in rosemary – in fact, both 1,8-cineole and camphor are also found in rosemary, though its repellent effect was found to be lower than that of lavender.

So, with some scientific evidence for lavender’s efficacy under our belt, what about mothballs? Why not use these to repel moths? The compounds behind their effects are little less of a mystery. Older mothballs used naphthalene, while today it’s more common for them to utilise 1,4-dichlorobenzene. Both of these compounds evaporate slowly from the mothballs, creating a gas toxic to moths and preventing infestations. Camphor, which as we have seen is present in lavender, can also be used on occasion.

The issue with naphthalene and 1,4-dichlorobenzene is the growing concern over the effects of long-term human exposure to them. Consequently, their continued use is being reviewed, and some countries have already banned naphthalene from use, including countries in the EU. It’s perhaps encouraging, then, that dried lavender seems to show suitable repellent properties to act as a replacement!

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This article was originally published on the Compound Interest website under a Creative Commons Attribution 4.0 International License. Read the original article here.

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