How to Stop Guessing at the Essential Oil Usage Rate When You Make Soap

Now that I've dished on my top ten recommended essential oils for soapmaking, I want to dig into the age old question of:

How do I figure out the usage rate of XYZ essential oil? How much essential oil do I use in soapmaking?

Unfortunately, this is never a straightforward answer, but let's decipher the in's and out's of essential oil usage rates in soapmaking!

Converting your essential oil usage rates from percentage to weight

For most cosmetics formulating, fragrances are used at a rate of 0.5% to 5% of the total formula: less for leave-on products, more for wash-off products, and even more for non-skin contact products.

As cold process soap is a wash-off product, the standard essential oil usage rate falls in the mid-range. I generally use an essential oil usage rate of 2% to 4% of my soaping oils.

For example, if your soap mold holds roughly 4 oz of oil per cavity (giving you 4.75 oz bars of soap), a 3% usage rate would be found like so:

4 oz x 0.03 (3%) = 0.12 ounces or roughly 3.5 grams of essential oil

Notice how the essential oil usage rate is calculated from the oil of the formula, and not from the total. Why is that? In soapmaking, we use water (or other liquids) as a carrier for the sodium hydroxide (lye) to complete saponification. After saponification is complete, the water mostly evaporates from the formula during cure. If you calculate your essential oil usage rate based on the total formula, it will become more concentrated during cure - not good!

As a side note: I have never used drops for anything as they are highly inaccurate and vary so widely (big drops, little drops, oops, an extra drop, etc.). I always weigh my ingredients, including my essential oils, in soapmaking - no drop, cups, or guessing!

Where this gets complicated with essential oil usage rates is that each individual essential oil poses its own unique challenges, guidelines and needs, due to possible skin irritation, sensitization, photosensitivity, and performance in soapmaking. Some essential oils have a lower recommended usage rate than others due to these issues.

Personal preference plays a part in deciding how much essential oil to use

Here are my personal maximum essential oil usage rate guidelines for soapmaking:

If you want to use an essential oil with a low usage rate, you can pair it with essential oils that have a higher usage rates. For example, creating a blend containing clove bud essential oil and patchouli essential oil together, which gives you a total of 0.58 ounces maximum (0.5 oz ppo patchouli, 0.08 oz ppo clove.) Your combined essential oil usage rate (the total sum of all essential oils) should not reach over 0.8 ounce to 1 ounce per pound of oils (5% to 6.25% of the oils.)

Each of these maximum essential oil usage rates for soapmaking were pulled from my personal reference sheet, calculated based on experience, strength of scent, and standards compliance. I prefer my products scented in a mild to moderate amount, so you may choose to use a higher essential oil usage rate based on your preference.

I briefly checked each essential oil usage rate against current IFRA Standards (48th Amendment) using my personal stock of essential oils and their specific information to the best of my ability. (I'm not perfect and will add any corrections as necessary, please continue reading to learn how to check the standards yourself!)

Wait, what are IFRA Standards?

Yessum, there is yet another layer to calculating your essential oil usage rate! The International Fragrance Association (IFRA) Standards work to regulate the safe use of fragrance materials that are skin sensitizers and irritants.

The International Fragrance Association establishes guidelines for safe usage, and works with the Research Institute for Fragrance Materials (RIFM) to determine these guidelines based on scientific analysis rather than unconfirmed reporting or speculation.

This is starting to sound complicated, right? To make safe essential oil usage rate info more accessible to to the soapmaking community, I've created the EOCalc. With this tool, you can calculate safe usage rate for your own essential oil blends or you can explore fragrance blends from my personal formulary and submissions from our group. Check out everything to EOCalc can do for you!

Compliance with the IFRA standard are on a volunteer basis but are recommended. While membership of the IFRA is usually out of reach for white cottage manufacturers (such as you and I), the standards and practices recommended by the IFRA are open for public viewing and understanding.

The IFRA Code of Practice and the IFRA Standards Booklet are available on IFRA’s website: http://www.ifrafragrance.org

Three IFRA Standards classifications affect essential oil usage rates

• Prohibited means that you should not use the ingredient at all.
• Restricted means that you can use the ingredient, however, it should only be used below a certain concentration level.
• Specification means that you should evaluate purity criteria.

IFRA Product Categories also determine essential oil usage rates

And there are eleven categories of product types that are used to determine safe usage rates, they are as follows:

• Category 1: Lip Products, such as lipstick, lip balm, lip scrubs
• Category 2: Deodorant and antiperspirants
• Category 3: Hydro-alcoholics for Shaved Skin, which include eye products, men’s facial care products, and products for children or infants
• Category 4: Hydro-alcoholics for Unshaved Skin, which include some hair products, body mists, body lotions, body oils, foot care products, and fragrance ingredients in cosmetics and perfumery kits
• Category 5: Facial care products, facial masks, hand cream products, dry shampoo, and permanent hair products
• Category 6: Mouthwash, toothpaste, or sprays
• Category 7: Insect Repellents
• Category 8: Makeup remover, hair styling aids, nail care products, and any powder or talc products
• Category 9: Wash-off products such as soap, bath gels, body washes, shampoo, conditioner, liquid soap, or shaving cream
• Category 10: Laundry detergent, fabric softener, and household cleaning products
• Category 11: Non-skin contact products that may come in contact with skin, such as air fresheners, candles, and reed diffusers

Before using any essential oil in any product formulation, you should check the IFRA Standards for compliance on usage rates in specific product types. Unfortunately, this is becoming more difficult for the less knowledgeable formulator as many of the standards have shifted to listing by specific constituent rather than the complete essential oil. (That's why I created the EOCalc to help soapmakers at every level.)

For example, cinnamon leaf essential oil is a restricted material due to its eugenol content. In order to comply with the IFRA Standards, you must know the eugenol content of your cinnamon leaf essential oil to determine the safe usage rate in your product category (if it's soap, that's category 9 and the max eugenol content is 0.5% currently). The eugenol content of your essential oil can be found on either a CoA, (M)SDS or GC Analysis of the essential oil from your supplier, and it can vary from batch to batch and crop to crop.

It's important to note that each individual batch and crop of an essential oil can contain differing levels of constituents, so you will need to check your specific essential oil. For example, New Directions Aromatics currently lists their cinnamon leaf essential oil as 82.8% eugenol, but the cinnamon leaf essential oil I currently have on hand contains 77.2% eugenol. Because eugenol is the restricted material and not the whole essential oil itself, your maximum usage rate will be slightly different than mine.

For the EOCalc, each essential oil profile was created from a sample of actual GC/MS analyses performed on essential oils that have entered the marketplace, GC/MS analyses from scientific literature and studies, and reputable research sources, such as Tisserand’s Essential Oil Safety. For more details, check out the EOCalc's Frequently Asked Questions page.

Now, you wouldn't want to use more than 0.5% of cinnamon essential oil in cold process soap anyways, as more than that will accelerate your soap beyond most reasonable amounts for a soapmaker!

Thankfully, great essential oil suppliers are extremely knowledgeable about the products they sell in regards to restrictions and can usually answer any questions you may have. Many even list standards compliant essential oil usage rates on their website, so you can skip the math!

Want to learn everything about using essential oils in soap and cosmetic in one place? Grab a copy of my book Smellgoods: How to Use & Blend Essential Oils in Handmade Soap & Skincare.