Wednesday, March 23, 2011

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 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, have high flash points 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 becomes difficult or impossible to pour.  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 60 seconds.  You gotta be ready to move fast! 

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.  Many of the more popular essential oils, on the other hand, average around $3.00 per ounce, and some (jasmine or sandalwood, for example) cost hundreds and even thousands of dollars per ounce.  Essential oil scents also tend to fade faster.  Citrus oils can be 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, crisp, clean and slightly astringent scent of cucumbers, for example, but there's no such thing as cucumber essential oil.  You can also get fragrance oils that are imitations of popular designer perfume and cologne scents, which some folks really love.

An open question is whether one is safer for skin contact than the other.  Essential oils are derived from natural sources, but some are known 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 phthalates used in fragrance oils and many plastic products have been linked to a number of health risks, but most fragrance oil manufacturers that used them 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 thing or a 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 I so enjoy experimenting with new scents and scent blends, using both natural and synthetic fragrances. 

One customer told me she absolutely loved a soap she bought that smelled like leaves burning in the fall.  I personally can't imagine wanting to use a soap that smells like anything that's burning, but I totally understand that she has her own special connection to that scent, and that's all that matters.