This article, looks at how essential oils (specifically some citrus oils) change over time if exposed to air and the more volatile components are allowed to evaporate.
The research was done by passing a steam of nitrogen through the essential oil and then measuring the chemical composition of the oil at regular intervals.
With Lemon oil, it found that the concentration of Citral, one of the compounds more likely to cause sensitisation of the skin increased over time. With Sweet Orange, it found that by the time only 10% of the essential oil was left it was close to 100%limonene.
This clearly has implications when some forms of distribution of the oils are used to disperse them into the atmosphere. What it doesn’t tell us is how things change between using a burner where the oil floats on water warmed by a candle, a nebuliser diffuser where air is bubbled through water with the oil sitting on top and an electrostatic diffuser.
The other area where it tells us we need to be careful in the storage of our essential oils. If caps are regularly left off citrus oils there is the potential for the more volatile compounds to evaporate leaving behind ones that are more likely to cause skin reactions.
Possibly the greatest risk in this is Bergamot with it’s risk of photo=sensitisation. With susceptible individuals exposure to the sun or artificial uv rays can cause severe sun-burn if the exposure occurs within eight or twelve hours depending on which book you read. Even in winter I warn my clients about this risk though I have yet to have one admit to using sun lamps! I have also yet to see an adverse reaction of this type.
As well as keeping the top on bottles of oils except when dispensing, it is also important to only buy bottles of citrus oils that will be used up in a reasonable period of time.
What would have been more useful to me would have been some assessment of how the oils evaporate during a treatment. (Mine last up to a maximum of two hours.) Does the presence of a carrier oil which the essential oils are diluted in for massage greatly reduce the amount of evaporation as I suspect or not?
I have flagged this up in a number of different forums so it is likely that if this research has been done someone will let me know.
On a final note, while we may have had the UK’s warmest November day ever this week, the summer as a whole has not been of the highest risk for sunburn with or without sensitisation from inappropriate use of essential oils!