What is limonene?
So you’ve heard about limonene being used in cleaning products, and you want to know what this stuff is and whether it’s safe. Well, here’s our lemon-scented guide to this often maligned chemical.
You know that delicious, fresh smell you get when you slice open an orange, lemon or lime? Well, it’s mostly limonene, and it doesn’t just smell nice; it's also useful and safe. That’s why it is used in products designed to clean your home.
Limonene is a naturally occurring compound found mainly in the skin of certain plants and fruits, including lemons and oranges. It is used in cleaning products for two reasons: it has a pleasant, lemon-orange smell, and it acts as a solvent to help clean.
It is from a large family of natural substances called terpenes, and it has no colour and its toxicity is low. However, you might have heard about it recently because, when it reacts with ozone in the air, it undergoes change which releases tiny amounts of other compounds, including formaldehyde.
Peeling an orange releases orange oil into the air. As orange oil is 90% limonene you can get more exposure by peeling an orange than from using cleaning products.
Found in a vast array of cleaning products, cosmetics, food flavourings and even aromatherapy, it comes in two forms: d-limonene and l-limonene. These are like “different handed” versions of the same molecule, with only subtle differences.
The d-limonene form is used in food-grade products, as well as cleaning and beauty products, and is prized mainly for its smell. It is also used in hospital laboratories when cleaning tissue samples for analysis.
The l-limonene version has a more pine-like scent but is used mainly as a solvent in industrial cleaning products.
Apart from these well-known uses, researchers now also believe limonene could be used as a dietary supplement to prevent cancer. It even turns up in some 3D printing processes.
The good news is that limonene itself has low toxicity, which is why it is used so widely in food-grade products. It's sometimes referred to as a volatile organic compound (also known as a VOC), but then again almost everything you smell is a VOC.
However, it can react with ozone, which is a common compound in the air. Though hazardous, the amounts of formaldehyde formed even in homes where a lot of cleaning products are used will be well below the safe levels established by the World Health Organisation (WHO). Check out our guide to formaldehyde in indoor air if you want all the details.
There have been some reported cases of skin sensitisation, but these have usually developed in those involved regularly with pure limonene in an industrial setting for paint preparation or degreasing machinery.
Where do we get it from?
One of the positive aspects of using limonene in cleaning products is that it is a renewable product. Manufacturers extract it from the skin of citrus fruits by two methods: by spinning liquefied citrus rind (centrifugal separation) or by ‘cooking’ the rind (steam distillation).
Limonene is a useful compound and pleasant to smell. It is a renewable resource and is considered to have very low toxicity, and is even being studied as a possible dietary supplement to prevent cancer. Although it can react with ozone in the air to produce tiny amounts of formaldehyde for a short period of time, those amounts are considered by the WHO to present negligible risk.