Things I can safely say:
- There is no evidence of benefit from any of these chemicals, EO or FO, outside of their well known uses. Cineole, for example, from eucalyptus oil, is a well known toxin (we had significant protections from it at work) but it works well for clearing the sinuses.
- There is a massive difference in the concentration of products applied to the skin versus the quantities that are volatilised and inhaled.
- Application to the skin is not a natural thing to do so whether the product is naturally or synthetically derived is pretty much irrelevant to any discussion of potential harm. Although to take the example of limonene, the natural derivation would include a number of additional chemicals, each of which may introduce additional risks.
- This discussion can easily wander into chemophobia. While I like to apply a precautionary principle and limit my exposure to unnecessary chemicals, in the absence of evidence of harm no real conclusion can be drawn on each chemical, either natural or synthetic. It is up to the individual to gauge whether the risk is worth it to them. It will take decades for medical research to draw any real conclusions about any of these chemicals, just like it took decades for tobacco smoke to finally be accepted as the massive carcinogen that it is...
A parallel can also be drawn here with alcohol. We know there is no real evidence of benefit (any benefit from red wine being attributable to the polyphenols from the grapes so it is likely better to just eat the grapes instead!). We also know alcohol is the most harmful drug to society as measured by economic cost. The potential for and mechanism of harm in this case is very clear to see.
Some people can manage the risk of exposure but many can’t. Is it really worth the risk when teetotalling can avoid it entirely? Everyone has a different answer to that... for myself I have given up the booze but I still enjoy riding motorbikes - to each their own. And I try to buy unscented products these days - but the scents really never did anything for me anyway...