Tuesday, December 27, 2011

Essential oils: Peppermint - the science relating to menthol

Peppermint essential oil is composed of 38% to 48% menthol (a monoterpene alcohol), 20% to 30% menthone, and about 6% 1,8-cineole (aka eucalyptol, which we discussed in the post on eucalyptus!) Menthol is the most interesting part of peppermint as it's the compound that gives us that cooling sensation we seek when we add it to our products.

As I mentioned the other day, menthol and 1,8-cineole react with a temperature transient receptor (TRPM8) that we find on our skin and in the nasal vestibule (the thing we call our nose in this elaborate picture to the left). When we use menthol as a decongestant, it's a sensory illusion. There's no change in the amount of air we can inhale or exhale, it just feels like there's less resistance. 1,8-cineole and camphor offer these same sensations.

In an early study (Packman & London, 1980), they found inhaling menthol was effective at reducing cough frequency in people who had citric acid induced cough (a reminder as to why we should wear masks in our workshops!). It wasn't as effective as 1,8-cineole (or eucalyptol), but it was more effective than the placebo. In another study (Keria et al, 2008), menthol was found to be effective at reducing cough frequency, but it wasn't as effective as the placebo. But here's the problem - the placebo was eucalyptus oil, which has been shown time and time again to reduce cough frequency. So how can we trust this study when the authors thought that something like eucalyptus oil was an effective control? Unfortunately, the other study I could find on this topic - click here - had volunteers inhale 75% menthol in eucalyptus oil! So how do we know if it's the 1,8-cineole or the menthol that worked well?

This really does show you that you need to read more about the study than just the results! What is wrong with with these researchers? Are you studying menthol or eucalyptol???

Why is it (possibly) effective for coughs? It could be because of menthol's interaction with airway cold receptors - apparently our body likes colder air - or with the neuronal cough reflex.

With the digestive stuff, our products wouldn't be really all that effective unless you were eating them and you were using peppermint oil in huge doses. But we can make someone with a cold feel a little better by making something containing peppermint oil or menthol they can huff...I mean, sniff. For instance, making a blend of essential oils someone could breathe in straight from the bottle or put into the reservoir of a humidifier might be a nice thing indeed. I like to make a blend of 1 part eucalyptus, 1 part peppermint, and 1 part camphor and put a few drops into the holder on my humidifier. And I keep a small bottle of this beside my bed so I can smell it regularly. I also put some foot lotion with the Vicks' blend (3 parts menthol, 1 part eucalyptus, and 1 part camphor or 3 parts peppermint, 1 part eucalytpus, and 1 part camphor) on my chest so I can inhale its awesomeness when I need to breath easier (although we know it's an illusion, it still feels good!)

Click here for some ideas for products in which you can use peppermint!

Join me tomorrow as we take a look at some of the other awesome benefits of peppermint oil!

No comments: