I remember when I first started getting into essential oils in early high school, I used peppermint in a blend and was pleased to feel that distinctive hot-cold tingle on my skin. I used the same bottle (a 1 oz. size) on occasion for several years, and gradually, that tingle disappeared. I thought it was just my body acclimating to the peppermint every time that I used it, but imagine my surprise when, after purchasing a new bottle of peppermint oil, the tingling sensation returned! What had happened? The peppermint oil I had been using still smelled like peppermint and seemed to be totally fine and not rancid or spoiled at all, yet over the years it seemed to have lost some of its efficacy.
The truth is, essential oils do have a certain span of time in which they are most potent. Oils are complex chemical compounds made up of multiple organic molecules ranging from esters to alcohols, some of which are more volatile than others and some of which break down more quickly. The peppermint that I had been using for all those years was no doubt running low on the organic compounds that traditionally give peppermint its characteristic tingle on the skin, even though it still smelled just as fresh as the day I first opened it.
So what’s a good rule of thumb for purchasing and using essential oils? Well, it really depends on the oil. Some of them have shelf lives of up to three years and can be used effectively within that amount of time. Others have shelf lives of as little as a year and need to be used quickly. A general rule that I follow is that for oils which have a shorter shelf life, I buy smaller bottles. This way, even if I go through the oil more slowly, I can still ensure that I’m not as likely to waste anything that is left over by the time the date passes. For oils that I use very frequently, such that I know that they will be used up quickly, or that have a longer shelf life, I buy slightly larger bottles. This is probably the most common error that those new to the essential oil world make. Not realizing how very little oil they need to use for various therapeutic applications, they buy larger bottles and find that their money is wasted in a year or two when the oil is no longer as effective and they still have half the bottle to go. So buy small at first! You may end up using lots of that oil and decide to upgrade to a larger bottle later, but for a first try, always opt for the smaller size.
The other important thing is to label your bottles somehow so that you know when the oil was purchased and when it was opened. This will help you better keep track of which bottles are approaching the end of their effective shelf life so that you know which ones you may need to either use up quickly (or reserve for only diffusing, which I will cover in a moment), as well as which ones you may need to order again.
Another rule I have is that, even if an oil is no longer useful for physical therapeutic applications, such as massage oils or similar blends, I still don’t throw it out unless it is very obviously rancid or stale. I will, instead, use it in a diffuser or in another manner in which it can be easily inhaled, since the scent generally stays fairly potent and can still provide overall aromatherapeutic benefits. It's an easy, natural way to scent your home or office without having to turn to artificial air fresheners, and it gives you a good way to use up your older oils. Also, while I’ve never made soap myself, I would be willing to wager that you could even add “expired” oils to your soaps to lightly scent them. It never hurts to be creative!