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One of the more popular topics on web sites that advocate for natural cures is the cornucopia of purported benefits ascribed in some way to leaves from the bay laurel (Laurus nobilis). Blender spokesperson and gravity skeptic David Avocado Wolfe, who runs a pseudoscientific alternative health and supplement empire, made this claim about burning the leaves on a widely shared post on his eponymous web site: It is interesting that Wolfe selected this specific article to support the assertion that burning a bay leaf works to reduce anxiety, as that study actually concluded — using laboratory rats — that while linalool can decrease motor function and essentially knock a rat unconscious at excessive doses, it does not appear to have a strong anti-anxiety effect: That does not mean, however, that there were a dearth of papers Wolfe could have selected that suggest a connection between linalool and anxiety, merely that his review of the scientific literature appears to have been both extremely superficial and largely incomplete. Linalool is a major component of many aromatic plants, most notably lavender, and it has been the subject of a number of different areas of research. A better study (in terms of results but not necessarily methodology) for Wolfe would have been a 2010 paper published in the journal Phytomedicine, which suggested (using laboratory mice and pure linalool vapors) that linalool may have an effect on anxiety: The light/dark box test, which investigates how quickly a laboratory mouse leaves a dark space to explore a novel light space, is a controversial method to assess anxiety, however, as it is prone to false positives and many do not consider it an accurate analog for human anxiety. This test was also performed in other animal studies related to anxiety and linalool that provide evidence for a connection. In terms of human studies, a study published in the journal Human Psychopharmacology in 2009 reported results from the administration of lavender capsules (which, again, contain linalool) to 97 individuals while showing them a combination of neutral and anxiety-producing films. They concluded: Whatever one's reservations are about the methodology employed here, it is important to note that lavender capsules are not bay leaf vapors, even though both likely contain linalool. Lavender oil contains between 25 to 38 percent linalool, whereas the oil derived from bay leaves contain around 4 to 6 percent linalool, and ingestion versus inhalation involve different processes in the body. It is also important to distinguish between the overall effect of smelling a pleasant aroma such as bay leaf smoke or lavender vapors, which can have a general effect on mood, from the specific biochemical mechanism by which substances may affect mood. Rachel Hertz, a professor of Psychiatry and Human Behavior at Brown University who has studied the interplay between mood and smell extensively, explained in a piece for Scientific American that the most obvious mood-scent link is through associative learning, which she says is especially powerful for the sense of smell: Teasing apart this kind of effect from from any more specific biochemical method is challenging, and none of the research on linalool or lavender oil is adequate to address the possibility that bay leaf smoke could have a marked effect on anxiety. As such, we rank the claim that bay leaf combustion serves to reduce anxiety as unproven.
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