Essential oils are complex mixtures, often containing over 100 components including saturated and unsaturated hydrocarbons, alcohol, aldehydes, esters, ethers, ketones, oxides phenols and terpenes. This can make them a real headache in terms of safety assessment. Some of our recent work has led to more in-depth investigation of this topic – it’s both fascinating and challenging!

Essential oils are extracted from the flowers, barks, stem, leaves, roots, fruits and other parts of plants and are sought after by the cosmetic and pharmaceutical industries for a wide variety of reasons. Because of their characteristic odours, they are popular for use in fragrances, skin, hair, body and face products as well as massage oils and insect repellents. This means that they are frequently applied directly to the skin, put into bath water or inhaled.

At XCellR8, we are most commonly asked to assess their irritancy potential to the skin and eyes, as well as whether they can cause skin sensitisation. Essential oils containing certain compounds also need to be tested for phototoxicity and genotoxicity, which is where our findings became so interesting.

Different genotoxicity classifications for the same oils

We have found that essential oils from different suppliers can yield different genotoxicity classifications in vitro – something we as an industry cannot take lightly. There’s increasing published evidence that the composition of essential oils and absolutes can vary according to so many factors, including:

  • Extraction process (eg FENNEL)
  • Geography: variations in soil, climate and air quality (eg ROSEMARY)
  • Altitude (eg TEA TREE)
  • Harvest season (eg MINT)
  • Age of the plant (eg GINGER)
  • Position of the leaves on the stem (eg SWEET BASIL)
  • Plant species and varieties (eg LAVENDER)

As well as these harvesting factors, how the essential oil is then treated can also impact its performance. Some oils are adulterated or diluted when processed, but this can be difficult to identify. How they are packed, stored and handled can also have an effect; chemical degradation can occur with exposure to heat, light or oxygen. Essential oils from citrus products are especially prone to oxidation that can quickly alter the chemistry of those essential oils.

Are current testing guidelines over-simplistic?

Formal sources of guidance eg the International Fragrance Association (IFRA) provide a single view for each raw material, but our work and other recent research suggests that this may be over-simplistic, highlighting the need for different sources of the same raw material to undergo independent safety assessment. How can this be achieved in practice within realistic budgets and timescales? Could industry initiatives help to streamline affordable testing for essential oil suppliers? As ever, we’d love to hear your thoughts.