Glossary
A cyclic monoterpene that is the dominant aromatic compound in citrus peels (comprising 90-97 percent of orange peel oil), widely used as a fragrance ingredient in cosmetics and cleaning products, and found naturally in bee propolis. Limonene is classified as a potential skin sensitizer in the EU, requiring labeling when present above certain thresholds.
Limonene is one of the most common terpenes in nature. Beyond citrus, it occurs in many essential oils (lemongrass, dill, caraway, celery), herbs (rosemary, mint), and tree resins that bees collect for propolis. In products, it contributes a clean, fresh, citrusy scent that consumers find pleasant and which signals cleanliness.
As a chemical compound, limonene has documented degreasing ability (it dissolves oils), antimicrobial properties, and anti-inflammatory activity. It is used as a natural solvent in cleaning products and as a fragrance in personal care.
Fresh limonene has low sensitization potential, but when exposed to air, it oxidizes into limonene oxide and limonene hydroperoxide, compounds with significantly higher sensitization risk. This is why some people can tolerate fresh citrus essential oils but react to old or improperly stored ones.
The EU requires limonene to be declared on product labels when present above 0.001 percent in leave-on products or 0.01 percent in rinse-off products. This labeling requirement reflects the sensitization potential of oxidized limonene, not toxicity of fresh limonene.
Fresh, properly stored limonene has low irritation potential for most people. The concern is with oxidized limonene, which forms when citrus oils are exposed to air over time. Use fresh citrus essential oils, store them properly (sealed, refrigerated), and replace them every 6-12 months.
Yes. Propolis from temperate regions contains limonene along with other terpenes, contributed by tree resins. The concentration varies by botanical source and region but is typically lower than in citrus essential oils.
Only if you have a documented sensitivity. For most people, limonene in properly formulated products (where oxidation is minimized) is safe. If you experience redness, itching, or irritation from citrus-scented products, limonene sensitivity is a possible cause.
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