Essential oils and plastic: a compatibility to check
A few drops of essential oil are enough to scent a room. Sometimes they are also enough to soften a stopper or cloud a bottle. With these products, material is not chosen from a catalogue.
By Tecmom editorial team · 2 min read
Concentrated, volatile products
An essential oil is a mixture of volatile, hydrophobic organic compounds extracted from a plant, often rich in terpenes such as citrus limonene. That is what gives it its scent, and what makes it aggressive: these molecules are small solvents.
They can therefore migrate into plastic, swell it, weaken it, or escape through the wall. Reference works point it out: essential oils can be aggressive toward rubbers and plastics.
Not all materials react the same way
Studies on limonene, one of the most common components, show clear differences. In a study on orange juice published in Food Additives & Contaminants, low-density polyethylene readily absorbed limonene, while PET and polycarbonate took up only very small amounts.
That is why pure oils are most often packed in glass, and why diluted products, a scented cream or lotion, are more readily packed in plastic, after testing.
What gets tested
Compatibility is checked with the real product, in the real bottle:
- material behaviour: deformation, cracking, loss of stiffness in contact with the product;
- product loss: a fragrance evaporating through the wall or getting fixed in the plastic;
- closure tightness, liner and cap included;
- light protection, when the product needs it. See amber bottles.
In the European Union, a cosmetic product's safety report must also include information on the packaging material.
Choosing methodically
The rule is simple: the higher the essential oil concentration, the stronger the evidence must be. To compare the usual plastics, see our advice page HDPE, PET, PP and cosmetic packaging.
An essential oil forgives no approximation. The right bottle for it is not the one that looks most like it, but the one that has passed the test with it.
Glossary
- Essential oil
- A mixture of volatile compounds extracted from a plant.
- Terpene
- A family of odorous molecules common in essential oils.
- Limonene
- A citrus terpene, often used to test how plastics hold up.
- Sorption
- Penetration of a substance into a packaging wall.