What is Limonene?

Chris - Brilliant. Yeah, well limonene, it's the stuff that makes oranges and lemons smell orangey and lemony. So, if you take an orange and you scrape the peel a little bit and smell your fingers, it's that very intense orangey citrus smell, isn't there?Don - Yeah.Chris - And that is the limonene. The orange peel contains huge amounts of it. It's a very big organic molecule. It's lots of carbon and hydrogen atoms stuck together in giant ring structures. And in fact, we did an experiment on The Naked Scientists a little while back. Dave did it as a Kitchen Science where you actually blasted some of the limonene through a candle by squeezing the peel of the fruit and you spurted the limonene into the flame.Dave - That's right. You produce a sort of aerosol of limonene into the flame and limonene is really flammable and so, it catches fire.Chris - But the reason that fruit makes it is because it's also quite nasty for things other than humans who haven't got fingers to peel an orange. If you try to borough through the peel of an orange, you'd have to eat the peel and the peel doesn't taste too good. Limonene is mildly toxic and being organic and unpleasantly tasting as it is, it puts off insects and that's a way that the tree uses of keeping its fruit in good condition.Don - Okay. I find it also in my shower gel. Why is it in there?Chris - Sure. Well the answer is rather than trying to invent artificial flavours and colourings and things which would do the same job as a molecule which is already doing the job very well in nature, sometimes it's easier just to use the natural product and then you can also have a marketing benefit because you can say, "Hey! This is a natural product. It's got limonene in it." So, rather than having to use orange flavored stuff or a small molecule that smells the same, then you can just use the natural product and then you get two bangs for your buck. So, what it's doing in your shampoo is contributing a nice orangey aroma and which also, because it's fatty and oily, it will stick to your skin quite well. It won't get washed off by the water and it leaves you smelling vaguely with a faint aroma of oranges. Have you noticed that?Don - Yeah. I have.Chris - Then we've got the answer right. Thank you very much, Don.