Scientific soap making part III: essential oils vs.fragrance oils

As I prepare to teach a couple of soap making classes in the coming weeks, one of the topics I'll be covering is essential oils vs. fragrance oils and the pros and cons of each in cold process soap making.  My clear preference is essential oils because they're natural and have beneficial properties that fragrance oils don't have.  But first, let's clarify what the difference is between the two.

Essential oils are natural scents extracted from the leaves, bark, roots, flowers, and fruits of plants.  Fragrance oils are synthetic blends of the aromatic compounds found in essential oils and elsewhere. 

Is one preferable to the other?  Strictly in terms of cold process soap making, it's a toss-up.

Essential oils have an edge in that they have benefits beyond just a scent.  Tea tree is a great example because its natural antiseptic, antibacterial, antifungal, and antiviral properties are well researched and documented.  Eucalyptus essential oil's value in relieving symptoms of respiratory infections can make it a beneficial additive in skin and bath products.  Many beneficial claims are made for other essential oils, although most are poorly researched and largely unproven.  Fragrance oils, however, have no such additional benefits. 

A field of Bulgarian lavender, considered by many to yield

the highest quality lavender essential oil.

It's a toss-up between essential and fragrance oils in that both can be problematic to use in soap making. 

A problem with some essential oils is that the temperature at which their scent vaporizes (i.e., the flash point) is so low it won't survive ordinary cold process methods.  Eucalyptus, unfortunately, is a prime example.  With a flash point of around 110 degrees F, it can only be used in a soap that is prevented from heating up and going through gel phase, and preventing gel results in inferior soap texture and appearance.  The Lavender Oatmilk bars pictured below are a perfect example of a soap that did not go through a proper gel,

See the rind-like appearance of the outer edge?  It's noticeably lighter than the center of the bars, and it has a somewhat chalk-like texture.  Bars like these I either use myself or give away.   
Fragrance oils, on the other hand, generally have very high flash points -- far higher than the temperature of soap in gel phase -- so that's not an issue.  The problem with fragrance oils is that some accelerate the saponification process and cause the soap batter to become so thick so quickly that it cannot be poured.  With some I've used, the window of time between when the fragrance is added and when the soap becomes so thick it glops out of the pot rather than pours is less than a minute! 

Fragrance oils have an edge in cost and lifespan.  With just a few exceptions, fragrance oils are less expensive than essential oils.  Those with which I've been happiest cost around $1.50 per ounce, and their scents hold up for years, both in the bottle and in the soap.  Essential oils, on the other hand, range from as little as $1.00 per ounce to hundreds and even thousands of dollars per ounce, with the average for many popular scents ranging between $1.50 and $4.00 per ounce.  Essential oil scents also fade faster.  Citrus oils are especially short-lived in soap, with noticeable scent degradation in as little as six months.

One thing I personally like about fragrance oils is that I can use or experiment with scents that are either too costly to buy as essential oils -- like jasmine and sandalwood -- or that aren't available as essential oils.  I do love the fresh, clean, crisp, slightly astringent scent of cucumbers, but there's no such thing as cucumber essential oil.  In the bigger picture, however, this is a mixed blessing.  Many scents that don't exist as essential oils are better off left unused in soap making, in my opinion.  Cookie dough.  Pumpkin pie.  I cringe.

An open question is whether one is safer for skin contact than the other.  Because essential oils are derived from natural sources, some are actually more likely than fragrance oils to trigger adverse skin reactions.  Lemon essential oil, for example, is known to be irritating or sensitizing to some people's skin, as are spice essentials oils such as cinnamon and clove.  Synthetic fragrance oils . . . well we usually don't know how safe they are because the compounds used to make them do not have to be itemized on product labels.  We do know that the phthalates used in fragrance oils and many plastic products have been linked to a number of health risks, and most fragrance oil manufacturers have reformulated their products to be phthalate-free.

But whether scents are natural or synthetic, their effect and power is something I find endlessly fascinating. 

I recently invited a friend to smell the scent blend I used in a new soap I formulated.  She sniffed and appeared to have no reaction at all, just a funny kind of blank look on her face.  

"It reminds me of playing with Barbies," she finally said, completely unable to say why, or even whether that was a good or bad thing.  The most she could add was that she didn't mean the soap smelled like a Barbie doll, just that it reminded her of playing with Barbies. 

Science can help to explain how we perceive and process scents, but it can't account for the uniquely personal associations we make with them or the emotions they trigger.  That is beyond both the art and the science of scent development.  And that is the reason every soap maker should continue to experiment with new scent ideas, natural and synthetic. 

One customer told me she absolutely loved a soap she bought that smelled like leaves burning in the fall.  I can't imagine wanting to use a soap that smellled like that, but I totally understand her special association with that scent.  I share it.  Fond memories of a simpler time.