The 21 janvier 2021

Making an Essential Blend for Diffusion

Making an Essential Blend for Diffusion
By Rhiannon Lewis, Director of Essential Oil Resource Consultants, 
Editor of "The International Journal of Clinical Aromatherapy" & Host of "Botanica" Events

The following content is intended for information purposes only. Before use, we recommend seeking the advice of a health professional specialized in aromatherapy and cannot be held responsible if taken without prior medical advice. 

I love formulating with essential oils for their use in diffusion - combining efficacy with a balanced aroma that is pleasant and safe to inhale. The scent of the blend can be personalised to enhance mood, promote relaxation and create a desired ambiance whilst the chemical components themselves may offer benefits such as deodorization or airborne purification.

Over the years I have come to appreciate that there are several factors to take into consideration for optimizing the formulation itself as well as for its destined use. What follows are some points to consider as well as tips for making a lovely blend of essential oils for diffusion this winter.

Points to consider:

Why are you wishing to diffuse essential oils? Is it for ambiance? For airborne disinfection? For deodorizing a space?

·        If you are wishing to create a pleasant scent in a space to enhance ambiance, then you do not need to diffuse a significant quantity of essential oil. In fact, the less you use per diffusion, the more you are likely to pleasantly enhance the ambiance! It may simply be the use of a couple of drops of your diffuser blend in a bowl of hot water (kept out of the reach of children or pets) added just before your guests arrive, or using a quality organic ready-made aromatherapy candle or even putting a few drops of essential oil with water into an ultrasonic diffuser and run for 20 minutes. In this situation, less is always more!

·        If you are wishing to diffuse in a sick room environment with a goal of potentially reducing the viability of infectious organisms and thereby reducing infection transmission, then diffusion may need to involve more quantity of essential oil and more frequent diffusion. Typically 15 minutes of diffusion every 3 hours is sufficient for this indication. For this use, an ultrasonic or nebulising diffuser is more appropriate.

·        If you are wishing to manage malodour or use essential oils for deodorizing a space, then it may be that diffusion is not always the perfect answer – instead you might consider making an alcohol and essential oil spray and using it intermittently when the need arises. Spray high into the air near the location of the malodour – be sure not to spray onto the skin or onto varnished surfaces. And more importantly, don’t forget that where possible – good ventilation and fresh air are always superior than using deodorizing fragrances!


What type of diffuser are you using?

There are many ways to diffuse essential oils ranging from a simple ceramic cold diffuser (ideal for ambiance in a small space) to a heat-based vaporizer (also used for ambiance), an ultrasonic diffuser (these often require water to be added, can be used for both ambiance and airborne disinfection for small to medium size spaces) or a nebulizing microparticle diffuser (perfect for airborne disinfection of larger spaces and for dispensing larger quantities of essential oil – they usually have an on-off timer function).


The size of the room and ventilation

Depending on the size of the room, there may be a diffuser appliance more adapted for your needs (see above). Be sure to talk to your diffuser supplier about your particular needs. What is very important is ventilation – to avoid the buildup over time of volatile organic chemicals that could eventually be problematic for your health – if you are regularly diffusing essential oils in your environment, then you should also be regularly airing that same space.


The duration of time you diffuse for

This point is very important as it concerns safety. There is never a reason to run an essential oil diffuser continuously over an extended period of time. Not only is it potentially hazardous - a volatile organic chemical load can build up in the environment, making you susceptible to respiratory irritation, headaches and even airborne contact dermatitis - but it is also a wasteful use of your precious essential oils!

Many diffusers have an inbuilt timer – this is very handy as it is easy to forget to turn your diffuser off. If your diffuser does not have a timer, you can obtain and use a separate plug-in timer. As a general rule, it is rare to need to diffuse for more than 20 minutes at a time, and rarely more than 4 times per day.


Are children or pets present?

Safety for children and pets is important when diffusing – be sure to locate your diffuser and your essential oils well away from where they can be picked up, knocked over or accidentally spilled, licked or ingested! Aeration is very important. If you have a child under the age of 6, then I would suggest only diffusing when they out of the room and then to air the space well before the child re-enters. If you have pets, be sure that they can always leave the room if you are diffusing essential oils. Never leave a child or pet unattended in a space where there is a diffuser running.


Does anyone have allergies?

For some highly sensitive individuals, inhaling diffused essential oil particles can trigger coughing, sneezing or, in extreme cases, may trigger an asthmatic attack. The person may also complain of itchy eyes or headache. Usually these reactions are related to inappropriate choice (some essential oils are airway irritants) and overuse (too long duration/ too high a dose) of essential oils. For some people, migraines can be triggered by exposure to strong scents.


What is the availability and cost of the essential oils I plan to use?

Diffusion, over time, consumes a relatively large quantity of essential oils. This represents a significant biomass of aromatic plants. Therefore, cost and availability are important points to consider. Typical diffuser blends are generally dominated by readily available essential oils that have excellent volatility (they are often rich in monoterpenes) and are available from sustainable plant sources. Typical examples include essential oils from several citrus, conifer and eucalyptus species. These often form the major bulk of the diffuser blend (usually over 50%) with more costly essential oils that shape the particular character and depth of the blend being present in smaller amounts.

I personally avoid blending with precious and costly oils such as rose, melissa or neroli – these go into my other aromatherapy applications rather than being ‘lost’ in the air! Similarly, essential oils that are thick, resinous and that have lower volatility are difficult to use in diffusion – these include oils such as patchouli, vetiver or sandalwood…they may be better suited to other modes of essential oil administration. It is not to say that they are never used, but they would represent minor ingredients in a diffuser blend, if at all.


What is the safety of the essential oils I plan to use?

Each mode of administration of essential oils has its own safety guidelines. For diffusion, as we have already seen, the amount of essential oil diffused as well as the duration of diffusion are important safety considerations. Additionally, some essential oils are difficult to safely diffuse in any concentration because they may cause airway irritation or airborne allergy. These typically include essential oils that are rich in phenols (thyme, oregano, savory, clove) or aldehydes (cinnamon bark, lemongrass, citronella). Mint oils such as peppermint or cornmint are also not advised. These aforementioned essential oils are never diffused on their own or form the major ingredients of a formulation, but, with care may be able to be included in very small amounts if required. Putting safety aside, these same essential oils usually also have a high odour intensity - another reason why they are usually included in small amounts in the blend otherwise they tend to dominate the overall fragrance composition.

With the above points in mind, here is a diffuser blend example to illustrate how a typical diffusion blend is formulated.

Festive cheer blend

The main purpose of this blend to provide some light and cheer during the winter months when people are confined to home, it is cold outdoors and the reduced luminosity can lead to lowered mood. So, basically, this blend aims to provide a pleasant-smelling ambiance to lift the spirits, and may be reminiscent of the festive period for some. The secondary goal of this blend is airborne disinfection as a number of essential oil components in this blend are also effective airborne purifiers.

As you will see, I have calculated in percentages as this permits me to measure the total blend in many ways: by weight, by volume or by drops as needed.

  • Sweet orange (Citrus sinensis)=40%
  • Silver fir (Abies alba)= 25%
  • Benzoin (Styraz tonkinensis)= 15%
  • Palmarosa (Cymbopogon martinii)= 15%
  • Nutmeg (Myristica fragrans)= 3%
  • Clove (Eugenia caryophyllata)= 2%
  • Total= 100%


You will see that this blend is dominated (65%!) by readily available non-costly essential oils from sustainable sources that have a good volatility (citrus and conifer). For me, sweet orange is familiar, cheery and never fails to bring a smile. It is almost universally liked. As a child, I used to always have an orange in my Christmas stocking so it always brings me festive cheer! I personally chose silver fir as my conifer because I love its delightful Christmas tree aroma but there are numerous conifers that I could have chosen from. It also reminds me of crisp walks in the open fresh air.

I chose benzoin as its sweet warm vanilla aroma is cosy, comforting and enhances the sweetness of sweet orange (note: benzoin is not an essential oil so be sure to source your benzoin well – preferably the resin is extracted along with organic alcohol rather than other solvent).

Palmarosa adds a rosy roundness to the blend (I could have used geranium – but this is precious and costly), smoothing off the edges and adding depth in aroma.

The nutmeg and clove essential oils are included to add a gentle warming spicy and mood-enhancing note to the blend – you will see that they only represent a total of 5% of the total formulation. At this level, they are subtle yet discernible, and they safely add their spicy warmth to the blend.

Note: The presence of benzoin and the combination of citrus with clove will make this blend cloudy! Don’t worry – this does not affect the aroma or efficacy of the blend itself.


So how does this blend translate from percentage into quantities and measurement?

If I were making up a diffuser blend ‘stock bottle’ and had the equipment to measure each essential oil in volume, I would begin with an empty 15 ml glass bottle and add the required volumes of essential oil/aromatics, calculated according to their relative percentage. This quantity (15 ml) is enough for multiple diffusions over the winter months.

Similarly, if I had a precision balance, I could weigh each essential oil according to their relative percentage to reach my desired total weight of the formulation.


15 ml empty glass bottle with integrated dropper cap:

  • Sweet orange 6ml
  • Silver fir 3.75ml
  • Benzoin 2.25ml
  • Palmarosa 2.25ml
  • Nutmeg 0.45ml
  • Clove 0.3ml


If I do not have measuring equipment, then I could also measure the same amount expressed by percentage into drops into an empty 5ml glass bottle. This method is less precise as the drop sizes for each essential may vary slightly but for a home-use diffuser blend, this is still acceptable. This quantity would be enough for approximately 10 diffusions:


5 ml empty glass bottle with integrated dropper cap:

  • Sweet orange 40 drops
  • Silver fir 25 drops
  • Benzoin 15 drops
  • Palmarosa 15 drops
  • Nutmeg 3 drops
  • Clove 2 drops

So how would I use this blend?

·        On a ceramic cold diffuser : 5-10 drops, renewed when the scent is no longer discernable.

·        On a heat source diffuser or fan-assisted appliance: up to 5 drops per diffusion period.

·        In an ultrasonic diffuser: 5 drops diffused for 15-20 minutes maximum, up to 4 times per day.

·        In a nebulizing microparticles diffuser: I screw the bottle into the diffuser and set the timer for 15-20 minutes duration.


Happy diffusing !