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PTSD, Olfaction, and Essential Oil Orange

Updated: Aug 1, 2021

Human and animal studies have shown that Citrus sinensis (#orange #essentialoil), has physiological and psychological effects that result in the decrease of fear, stress, and anxiety.

Posttraumatic Stress Disorder (PTSD) is a mental health disorder that can develop after a traumatic event. In Diagnostic and Statistical Manual of Mental Disorders: DSM-5, the American Psychiatric

According to the National Center for PTSD, 8 million people in a given year will be affected by symptoms associated with PTSD. (1)

Association defines the experience of a traumatic event as "exposure to actual or threatened death, serious injury, or sexual violence (2)". In the United States, "about 7 or 8 out of every 100 people (or 7-8% of the population) will have PTSD at some point in their lives.(3) Most people think of military personnel as the only group of the general public that are largely affected by PTSD due to their experiences during deployments in war-torn countries, but PTSD can affect anyone given the criteria.

PTSD Sufferers

#PTSD sufferers experience a range of symptoms such as chronic #insomnia associated with #nightmares, dissociative #flashbacks, #agoraphobia, #avoidance, #depression, emotional numbness, and severe #anxiety, to name a few. Environmental stressors such as persons, places, and certain smells and scents can abruptly trigger an emotional state for sufferers by reminding them of an aversive past incident.(4) Early studies focusing on the #olfactory system show "... that when a novel odor is paired with an emotional event, hedonic perception of that odor is altered in accord with the associated emotion.(5)" However, just as certain trauma-related smells and scents trigger fear-related memories for a PTSD sufferer, discovering appealing aromas that bring pleasant memories and calming emotions is certainly possible, and possible through aromatherapy.

#Aromatherapy is the use of concentrated plant extracts known as essential oils that are taken from herbs, flowers, and other plant parts to treat diseases. Citrus sinensis (Orange) is an essential oil that is steam distilled from the orange peel. It comes from the #monoterpene family and is considered a high note which means that its volatility, i.e., evaporation rate, is high. Proponents of aromatherapy claim the medicinal effects of orange essential oil help a client holistically, a view that is still met with skeptism by the western medical establishment. d-limonene is a primary chemical constituent in orange essential oil and has been attributed to being an antidepressant in massage (6) whereas the inhalation of d-limonene has an anxiolytic action (7).


#Olfaction is one of the five human senses and is simply the sense of smell. Yet, in its simplicity a dynamic, complex system exists. The olfactory system processes an odor or odorant molecule in the following way. An odorant molecule enters and travels up the nasal cavity. There the odorant molecule encounters the olfactory epithelium or membrane which holds tiny cilia that act as receptors. The odorant molecule binds to specific cilia on the olfactory epithelium that activate olfactory receptor cells. These cells in turn belong to G protein-coupled receptors (#GPCR). GPCR stimulates the formation of #cAMP (cyclic AMP), and this messenger molecule activates an ion channel that allows signal activation of the odorant receptor cell (7). From there, the odorant receptor cell is sent to its associated glomerulus. The electrical action response transverses into proteins and is sent from the #glomerulus down through the olfactory bulb. The chemical proteins arrive at the amygdala and use an alternative mechanism to arrive at the #orbitalfrontal cortex. Eventually, the action response reaches the hippocampus. "Unlike other senses, the olfactory neuroanatomy is intertwined via extensive reciprocal axonal connections, with primary emotion areas including the #amygdala, #hippocampus, and orbitalfrontal cortex (8)." Encoding thereby takes place in each region of the brain and associates the odorant molecule with a memory and an emotion.

The olfactory process amazingly assigns hedonic meaning to odor memory. Studies have shown that what is pleasant to some people incites something unpleasant in others. (9) In their research and discussion of three medical case reports, Eric Vermetten and J. D. Bremner stated that,

Odor memory is independent of other types of memory and is long lasting, with a resistance to decay over long intervals. This view, known now as "Proustian" view, also holds that odor memory is excellent for odors associated with significant autobiographical experiences. The relationship between olfaction and autobiographical memories appears to be stronger when the experiences are more significant and emotionally charged.(10)

For PTSD sufferers trauma-related odor memory can be detrimental and disabling as a particular smell can bring back aversive memories. '

Olfactory flashbacks can be disabling phenomena due to intrusive nature of memories. A wide variety of cues are mentioned as precipitants of flashback phenomena, varying from experiences with little and transient emotional disturbance to emotional responses that last longer and that evoke symptoms like anxiety, nervousness, nausea, and guilt. These symptoms can be mild but in some cases can be accompanied by dramatic fear and avoidance behavior.(11)

Further studies have shown as well that emotion-olfaction interaction can evoke negative mood states and turn innocuous odors aversive. (12)(13)(14)