Читать книгу Aromatherapy Workbook - Shirley Price - Страница 45

We now meet the carbonyl group again, =O, which attaches itself to a carbon on either a chain or a ring molecule, creating a ketone (see Figure 3.17).

FIGURE 3.17: a) menthone; b) acetone (ketones)

These are easy to identify as they always end in ‘one’. (N.B. A false friend is asarone, which is a phenolic ether in carrot oil.) A common one, not occurring in essential oils, but known to most people, is acetone (nail polish remover). Fortunately, ketones are not present in the majority of essential oils – I say ‘fortunately’ because many of them are not ‘user friendly’ and have to be employed with knowledge and care, as several are neurotoxic. There is no scientific proof that all ketones are hazardous and generally (and fortunately) those which are known to be very much so occur in oils not used by aromatherapists, e.g. tansy, buchu, thuja, rue, etc.

Oils used in aromatherapy which contain significant amounts of ketones are aniseed, caraway, hyssop, pennyroyal and sage, and in France, only pharmacists may sell hyssop and sage oils. It is thought that the ketone in hyssop (pinocamphone) may provoke an epileptic fit in someone predisposed to them and that a few ketones, e.g. thujone and pulegone, if used in overdose, may provoke a miscarriage.

At the EOTA conference (June 1990) at Brunel University, Dr K. Tyman said that ‘there are 4 different thujones and a change in molecular shape means a change in effect’. Dr Tyman made what I feel to be a most important statement, which explains why sage, supposedly very hazardous because of its high thujone content, does not in practice appear to be so.

He explained that because the thujone molecule can arrange itself in four different ways (alpha-thujone, beta-thujone, etc.) it is feasible to expect all four to have different pharmacological effects; therefore it may be that not all thujone molecule shapes will necessarily present a hazard.

Carvone, for example, present in caraway and dill oils (the latter is an ingredient in gripe water for babies), is assumed to have the hazards of all ketones, yet there is no evidence to prove this. In fact, it is believed that some ketones (like carvone) may be completely harmless. There are two forms of carvone, laevo-carvone and dextro-carvone, which may, as with the thujones, have different pharmacological effects. The properties of the two forms of carvone are different and they certainly have different aromas. Having said that, until further information comes to light we should take care with all oils containing ketones in any appreciable amount, just to be on the safe side – and it pays to know your chemistry!

Provided caution is exercised and oils containing ketones are well diluted (1–2 per cent maximum) and not used too often or for too long, their effects are calming and sedative, they break down mucus and fat and encourage the healing of wounds by the formation of scar tissue. Certain ketones are digestive, others are analgesic, stimulant or expectorant.