Citronellal - natural bug repellant

Have you ever burned a citronella candle to ward off annoying insects? Where do those come from and how do they work? These candles are often made using citronella oil - the essential oil from citronella grass, or Cymbopogon nardus. This oil is used extensively in soaps, perfumes, cosmetics, and of course candles. Interestingly, citronella grass is a cousin (same genus, different species) to lemongrass Cymbopogon citratus, used in teas and some recipes.

Inside citronella oil are several different chemical compounds, the most common of which is an aldehyde called citronellal (Fig. 1). This compound is a major contributor to the anti-insect and anti-fungal properties of citronella oil. When candles contain this oil, the heat from the flame helps the citronellal evaporate into the air - creating a bug-repelling zone all around the candle.

Figure 1: The grass Cymbopogon nardus, also known as citronella grass, produces oil that contains citronellal, a natural insect repelling compound.

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