A great many cosmetics and personal care products on the market contain an insecticide, and sometimes even the people formulating them don’t realise. To make things even scarier it is one of the very few things in cosmetic formulations that can penetrate the skin and get into the blood stream. I am talking about limonene. It isn’t added as an actual ingredient, but it is a component of some fragrances, orange oil, lemon oil and quite a few other essential oils.
Luckily, there is a bit more to the story. Limonene is a member of the terpene family, a charismatic bunch of molecules that seem to turn up all over the place in the natural world. It is the biggest single component of orange oil, which in oranges are concentrated in the peel. The way it works to kill insects, which I imagine is the reason the orange tree goes to trouble of making it in the first place, is simply to dissolve the waxy coating on their skin. Insects have a very different body plan to mammals like us. For a start they have very small bodies and so are at much more risk of dehydration than we are. A good solvent like limonene will damage their skin barrier and kill them.
Farmers often use orange oil itself rather than go to the trouble of purifying it. It is a neat idea isn’t it. A naturally occurring material that is harmless to humans but deadly to insects.
Limonene will also damage the skin barrier of a human in high enough levels, though not remotely fatally. Pharmaceutical scientists have investigated it as a skin penetration enhancer. I have done some work on this myself and can tell you that you need high levels to see any effect at all. It certainly won’t have any effect at the levels you would get in a cosmetic product, which would be less than 1% and usually a lot less.
Being a commonly occurring part of the diet, the body has the enzymes it needs to deal with limonene. Any that gets into your blood stream will be easily metabolised. Some people do find limonene to be irritating and it can cause allergies, but this number is extremely small.
In 1999 the EU’s Scientific Committee on Cosmetic carried out an extensive study of the risks of allergies with common fragrance components. Limonene didn’t make the list of the most likely causes of allergic reactions, but contact allergies were reported for it with the comment that it was mostly reported in the context of occupational exposure.
Knowing the way it works, it isn’t surprising that contact with large quantities of it would damage your skin. But at low levels for most people most of the time it is not going to do any harm at all. As the name suggests, limonene has a fresh lemony smell that is very hard to replicate. If you are one of the unlucky few who might react to it you are missing out on a very appealing smell – though you can still smell it of course. You will also find it easy to avoid as it is listed along with the ingredients on all packs.
The interesting thing for me is how easy it is to make something sound scary and dangerous when it is in fact, nothing of the sort. All you have to do is take a few facts out of context and you have a scare story good to go.
If you want to look into the safety of essential oils and fragrances a good place to start is the EU report I referred to earlier.
Thanks to Public Domain Photos on Flickr for the photo of an orange, the biggest source of limonene.