Hi all
if wondering about the toxicy of certain oils, i would recommend having a look at Robert Tissarand's Essential Oil Safety: A Guide for Health Care Professionals - it is rather expensive, so see if your library stocks it or ask on here -hp- to see if someone can give you chemistry info about wintergreen or other oils you're concerned about. the link below will take you to amazon, so you can see what the book looks like:
http://www.amazon.co.uk/exec/obidos/ASIN/0443052603/qid=1126858410/sr=1-2/ref=sr_1_26_2/202-7249736-6596633
Another good book is Aromatherapy: Essential Oils in Colour by Rosemary Caddy, which shouldn't cost more than £8 - it gives you a colour wheel with each oil, showing its chemical make up - although not having looked at it too recently, i don't know whether wintergreen is listed.
And Julia Lawless's Essential Oil Encyclopaedia, which contains a pretty comprehensive a-z listing of essential oils.
I'm currently still doing my ITEC holistics dip, and i'm certainly no expert on chemistry. however, a friend of mine on my course has recently finished her phd in chemistry and she said that used in small amounts, for short periods of time and for the right reasons there is no reason why you can't use the supposed 'toxic' oils. they are usually toxic in certain ways of application, as you know ingesting oils like eucalyptus up to 4ml has been known to kill - if you read the robert tissarand book mentioned above it will give details.
also, wintergreen is used in olbas oil, a wonderful decongestant that is widely available and has been used for years - you can also ingest a small amount from the olbas oil pastiles also widely available.
essential oil of wormwood, which is used in Absinthe, is known to be toxic but only in very high doses when ingested. Absinthe is still sold all over the world, the only difference is at what percentage of alcohol - it's only sold at 55% in the UK, but 70% in the Czech Republic - which is said to cause it's main toxic effects, which goes for any alcohol if drunk excessively and for long periods of time.
nutmeg is also an hallucinogenic, like wormwood, but can only harm when ingested in ridiculously high quantities. it can also leave you in a deep coma like sleep for more than 16 days according to what i've read - again robert tissarands book very helpful.
these are some of the oils they tell you not to use because of their toxic effects, but have they actually told you what effects they have and what doses cause them? Bergamot oil, for example, is also toxic, but no one tells you not to use it, because it is only mildly photo-toxic - it was used in sun creams not so many years ago, of which there is a reference in the Louise Tucker Aromatherapy book. it all depends on the oils chemical make up i would suppose.
for my course we had to do an assignment on the toxicity of essential oils we used and ones we wouldn't, of which we had no info from our college, we had to read books from the library and search the internet. i suggest, you might want to do a personal research project of something similar, so you get to know the benefits and the concerns relating to the essential oils you do use and some of the ones you don't e.g. wintergreen.
every aromatherapists experience with essential oils is different, and how each client reacts to them is also different. when looking in the books like the ones mentioned above and other aroma guides by shirley/len price or chrissie wildwood etc, most are based on their own personal experience as aromatherapists and therefore information differs. the same goes for aromatherapy tutors' experience, as they don't treat the same clients and the same ailments as each other. thus, trial and error, for want of a better phrase, plays a slight part in aromatherapy, as we don't instinctively know what the client is going to react best to - we try for synergy, but it doesn't always work. so we keep trying til something does work.
hope this is helpful,
love and ligh