Sensitization

What is sensitization?
Sensitization is a reaction to a substance which had not previously caused an adverse reaction.  This can present as redness, itchiness, burning, welts, etc. on the skin.  It can happen on the first use, but it more likely after multiple usages.  A great example is that a gardener may not develop a rash the first time he contacts poison ivy (highly sensitizing), but the second time he contacts it, his skin reacts with significant rash.

How does sensitization occur?
If you use any substance for too long, at too high of a dose, or too often, you may become sensitized to that substance.  In aromatherapy, this usually happens with topical applications.  For example, if a mild essential oil, such as lavender or tea tree, is used undiluted or even at a high dilution (say 50%) every day for several months, the risk of sensitization becomes high.  If it is used rarely, undiluted, the risk of sensitization is low. If it is used highly diluted (less than 5%) on a daily basis, the risk is low.  Once a person has become sensitized to a substance, like an essential oil, that sensitization is a life-long problem, requiring avoidance of that substance.

Which Essential Oils cause sensitization?
Some essential oils, such as cinnamon bark and oregano are considered to be "highly sensitizing", that is, it will cause sensitization in the majority of people unless used with proper dilution and respect.  Some are "moderately sensitizing", others are considered "non-sensitizing".  Lavender and tea tree fall into this last category.  However, that does not mean they should be used daily, undiluted.  It means that with proper dilution, it is unlikely to cause sensitization.

How to prevent sensitization?
First of all, always dilute.  For "non-sensitizing" essential oils, diluting at 10% is reasonable.  This means 10 drops of essential oil in 1 teaspoon of a carrier oil (such a coconut, avocado, grapeseed, or other fixed oil).  For highly sensitizing essential oils, some are recommended at less than 0.5%, which would translate to 1 drop of essential oil in 1 cup of carrier oil (as a rule of thumb).  One popular way to dilute essential oils for topical use is in a roller bottle.  In our lavender example, a 10% dilution in a 10mL roller bottle would mean 20 drops of lavender essential oil, then filling the rest of the bottle with a carrier oil.

Roller bottles are an inexpensive and convenient method of preventing sensitization.  Is sensitization still possible, yes, but has the risk been lessened, yes.

Diffusion

Essential oils are highly concentrated substances.  In some cases, thousands of pounds of plant matter are required to distill a single ounce of pure essential oil.  "Less is more" is a common reminder among aromatherapists to heed the strength of the essential oil.  

In general, inhalation is the safest way to use essential oils - and it is quite safe.  Inhalation can be as simple as a drop of EO on a tissue nearby, a drop in a bowl of water for steaming one's face, or a couple of drops in a high end diffuser.  Diffusion allows a larger space to be affected by a very low concentration of the scent.  

Is aromatherapy effective by inhalation and diffusion?  For certain uses, yes!  This method works because aromatic molecules, when inhaled through the nose, bind with olfactory receptors which lie very close to the limbic section of the brain.  The limbic area is the brain's seat of emotions and behavior. According to Jennifer Peace Rhind (2012),

Via the sense of smell and the limbic system, aromatics can act directly on the mind and emotions, and different odours will induce different states, such as sedation, stimulation, happiness, relaxation, apathy, depression, irritation, sensuality, euphoria, etc.  These effects will vary between individuals; therefore it is important to account for individuality when selecting essential oils for therapeutic use.

Studies have shown the effects of diffused rosemary and lavender essential oils on academic tasks.  These effects are not only measurable, but they are repeatable, giving scientific credence to the historic uses both rosemary and lavender.  

____________________

Buchbauer, G., Jirovetz, L., Jáger, W., Plank, C., & Dietrich, H. (n.d.). Fragrance compounds and essential oils with sedative effects upon inhalation. Journal of Pharmaceutical Sciences J. Pharm. Sci., 660-664.

Diego, M., Jones, N., Field, T., Hernandez-Reif, M., Schanberg, S., Kuhn, C., . . . Galamaga, R. (n.d.). Aromatherapy Positively Affects Mood, Eeg Patterns of Alertness and Math Computations. Int J Neurosci International Journal of Neuroscience, 217-224.

Rhind, J. (2012). Theoretical Perspectives. In Essential oils: A handbook for aromatherapy practice (2nd ed., p. 55). London: Singing Dragon.