Tuesday, January 3, 2012

Essential oils: Linalool

You see this compound listed on quite a few products, especially on products from the EU, but what the heck is linalool? Linalool is a monoterpene alcohol (also known as 3,7-dimethylocta-1,6-dien-3-ol) found in plants from the Lamiaceae family (mints, scented herbs), Lauraceae family (cinnamon, rosewood), and Rutaceae family (citrus fruits) (Wikipedia).

There are two stereoisomers of linalool - licareol or (R)-(-)-linalool, which is found in lavender, bay laurel, neroli, bergamot, and sweet basil. It has an odour described as "woody or lavender" (p. 171, Selected Topics in the Chemistry of Natural Products, Raphael Ikan). Coriandrol or (S)-(+)-linalool is found in coriander, palmarosa, petitgrain, and sweet orange flowers, and has an odour described as floral (p. 171, ibid).

I'll be writing more about isomers on Chemistry Thursday, so look for it! 

Linalool has been well studied with regards to sleep, reduction of anxiety, and analgesic properties. One study (Elisabetsky, 1995) found that there were "dose dependent marked sedative effects, including...increased sleeping time and decreased spontaneous locomotion in mice." (Handbook of Essential Oils, p. 301). Studies have found linalool may have a spasmolytic (muscle relaxation) effect and pain reducing effect on rats, as well as an anti-inflammatory effect (p. 718, Botanical Medicine in Clinical Practice and page 301, Handbook of Essential Oils). A study done on stress in rats found that "(R)-(−)-linalool inhalation represses stress-induced effects on the profiles of both blood cells and gene expression." In other words, smelling (R)-(-)-linalool reduced the expression of stress in rats. And studies of injecting linalool into rats to reduce inflammation has shown it can be effective (page 248, Handbook of Essential Oils).

It is not a given that if something works in rats or mice that it will work in humans, but there have been quite a few small studies on people for these effects, to the point where I feel comfortable in saying there's evidence to show that inhaling an essential oil with linalool may help with sleep. But there's certain point where I have to stop researching something. I have to stop researching here for the animal experiments as reading them is getting quite depressing. 

You will see linalool listed in the ingredient list on products from the EU (or Lush, in North America) because it's considered a contact allergen. When it is exposed to oxygen, it can break down into an oxidized product (click here for that study) that can provoke an allergic reaction in "over 5% of those who underwent patch testing" (click here for that information), and the author suspects that "about 2% of the complete population of Sweden are allergic to air oxidized linalool." (Interestingly enough, non-oxidized linalool didn't provoke the same response!) For a different take on this possibility, check out this abstract! "However, it remains to be seen how often such an allergy, once established, is responsible for any of the cases of allergic contact dermatitis commonly ascribed in the literature. Indeed, in some cases, patch test conditions may not be optimal for differentiating between clinically relevant and irrelevant allergy to linalool."

Why is it found in 60 to 80% of scented products (as per this web page)? Because of its flavour and fragrance properties. It smells and tastes pretty, and it's not that expensive to add to something like a dishwashing liquid or body wash.

Linalool has been shown to be good at killing mites: It's called an acaricide, which is are "pesticides that kill members of the Acari group, which includes ticks and mites" (p. 411 and 420, Bioactive Natural Products). "As a pesticide, Linalool is intended for use indoors to control pests (fleas and ticks) on pets and the spaces they inhabit by affecting the insect’s nervous system. Linalool is also used as an outdoor mosquito inhibitor..." (from the FDA handout), although there is some doubt about its efficacy for mosquitoes.

I would have researched the insect killing properties more, but it's giving me the creepy crawlies, so let's move on!!! 

I don't know much about labelling for commercial purposes, but if you're in the EU, you might want to check if you have to include information about linalool on your products. It's on the list of ingredients that must be declared, according to the Seventh amendment of the Cosmetics Directive.

Join me tomorrow for more fun with lavender essential oil!


Celine Blacow said...

Yes, in the EU, it's most definitely one of the 26 allergens and, if present above a certain level, it must be listed. The levels are 0.1% in wash off products and 0.01% in leave on products. All suppliers should provide an allergen declaration (which may or may not form part of the MSDS) and the producer must calculate these percentage based on the percentage of the allergen present in the final product. For example, it maybe that Linalool is present at 3% usage at a level of 0.12% in which case it does need to be listed for all products or, in another case it might be present at 0.09% in which case it doesn't need to be listed for wash off products but would need to be listed for leave products. It's easy once you know how to do the calculations!

Kristie Smith said...

What a fabulous article. Will make a blend of essential oils with high linalool for my aggressive, hyperactive six year old grandson to smell. Also explains why, on the Native American Nutritional's testimonials page for Palmarosa, two people suffered immediate redness and burning when it was applied.