Essential oils (EOs) are highly concentrated, aromatic plant extracts popular in aromatherapy and personal care. Their potency requires careful handling and storage to maintain efficacy and safety. A frequent question is whether plastic bottles are safe for these potent liquids, especially when diluted. The answer involves understanding the solvent nature of essential oils and their incompatibility with most plastics, which can lead to contamination and material degradation.
Chemical Compatibility: Why Essential Oils Degrade Plastics
Essential oils are complex mixtures of volatile organic compounds that act as powerful natural solvents. These compounds are primarily composed of lipophilic molecules, such as terpenes, aldehydes, and ketones. Terpenes are particularly aggressive toward conventional plastics.
When concentrated oils contact plastic, their non-polar molecules penetrate and interact with the long polymer chains forming the plastic’s structure. This solvent action disrupts the forces holding the polymer chains together. This causes the plastic to soften, swell, and lose structural integrity, leading to clouding, cracking, or warping. Common plastic types like Polystyrene (PS), Polyvinyl Chloride (PVC), and standard Polyethylene Terephthalate (PET) are highly susceptible to this chemical degradation.
Health and Safety Implications of Plastic Leaching
Degradation of the plastic container presents a dual risk: it compromises oil purity and introduces potential health hazards. As the essential oil softens and dissolves the plastic, chemical additives begin to leach into the oil mixture. These leached chemicals often include plasticizers such as phthalates and Bisphenol A (BPA), used to improve plastic flexibility and durability.
The resulting mixture becomes contaminated, posing a risk when applied to the skin or inhaled. Phthalates and BPA are recognized as endocrine-disrupting chemicals that can interfere with the body’s hormonal systems. Exposure to these foreign chemical residues also diminishes the oil’s integrity by accelerating oxidation, leading to a loss of aromatic and therapeutic properties.
Does Dilution Affect Storage Stability?
Dilution significantly reduces the concentration of aggressive solvent molecules, yet it does not entirely eliminate the potential for interaction. When essential oils are mixed with a carrier oil, such as fractionated coconut oil or jojoba, the carrier oil acts as a buffer. This spreads the reactive molecules across a larger volume, drastically slowing the rate at which volatile compounds attack the container material.
For high dilution ratios, such as common 1% or 2% topical blends, certain plastics may be acceptable for short-term storage or specific dispensing mechanisms. However, the solvent properties remain present, and long-term storage in plastic is strongly discouraged, even with dilution. Dilution with a water-based product is generally less aggressive than a carrier oil dilution, but the risk of leaching remains a concern for prolonged contact.
Recommended Container Materials
The most reliable option for storing essential oils, whether pure or diluted, is glass. Glass is chemically inert; it will not react with the essential oil compounds, preventing both contamination and container degradation. For optimal preservation, dark-colored glass, specifically amber or cobalt blue, is preferred because it filters out harmful ultraviolet (UV) light. UV exposure can accelerate the oxidation of the oils, causing them to lose potency quickly.
For situations requiring lighter or more durable containers, such as travel, select high-density plastics may be considered for short-term use with diluted products. High-Density Polyethylene (HDPE), marked with the resin code ‘2,’ and Polypropylene (PP) are generally more resistant to essential oils than other types. Metal containers, such as aluminum, can also be used, provided they are lined with an inert substance to prevent reaction with the metal. All containers should be tightly sealed to limit air exposure and stored in a cool, dark location away from direct heat.