What's the difference between essential oils and fragrance oils?
Short answer
Essential oils are natural volatile plant compounds; fragrance oils are lab-made blends with a stronger, more stable scent. Both work, but fragrance oils must be cold-process safe for soap.
Explanation
Essential oils suit cold and hot process soap once their stability at high pH is known. The safe range is 0.5–3% of batch weight, and the book's recipes use about 2%. Top and middle notes evaporate during saponification and curing, so the book recommends working near the upper safe limit and anchoring blends with base notes such as vetiver, patchouli, cedarwood or benzoin. Essential oil soaps smell milder.
Fragrance oils give a stronger, longer-lasting scent, but their soap compatibility varies. Non-tested oils can seize or rice the batter. In candles, the book uses the same 10–12% load for either.
What to do
- Pick one type per soap recipe; don't combine them.
- Check fragrance oils for vanillin, which turns soap brown.
Source: The Big Book of Homemade Soap, The Big Book of Sweet Dessert Candles — Fragrances and Colorants for Cold & Hot Process Soap · Cosmetic Properties of Essential Oils in Soapmaking