Castor oil is pressed from the seeds of Ricinus communis, a fast-growing perennial shrub native to tropical East Africa but now cultivated widely across India, Brazil, China, and parts of the Americas. India is the world's largest producer, accounting for the majority of global castor oil supply, and the source of the USP-grade extra virgin oil we use at Eternal Sunday.
Why it behaves unlike any other oil
Castor oil is structurally unusual. Around 90% of its fatty acid content is ricinoleic acid, a hydroxylated fatty acid found almost nowhere else in the plant kingdom at this concentration. This single characteristic explains nearly everything distinctive about castor oil's behaviour: its exceptional viscosity, its ability to remain on the skin's surface rather than absorbing through it, and its role as a natural emulsifier.
In practical terms this means castor oil does something most carrier oils can't, it binds water and oil together without synthetic emulsifiers, and it stays where you put it, forming a lasting protective film rather than sinking in and disappearing.
What it does in soap
In cold-process soap-making, castor oil has a specific and well-documented role: it boosts lather and makes bubbles more stable and conditioning. Even at small percentages its effect on the quality of the lather is noticeable. The bubbles become denser, creamier, and longer-lasting, particularly in combination with the high-lather contribution of coconut oil.
It also acts as a humectant in the finished bar, drawing moisture toward the skin during use. This is partly what gives a well-formulated natural soap its conditioning quality on rinse, castor oil is a significant contributor to that result.
What it does in body butter
In our body butter formula, castor oil serves a different purpose. It acts as a natural emulsifier and texture modifier helping the blend of butters and oils come together smoothly during production and stay stable over time. It also contributes a subtle slip that makes the body butter easier to spread, without adding heaviness or greasiness to the finished feel.
USP grade
USP stands for United States Pharmacopeia, a grading standard that indicates the oil meets pharmaceutical-level purity requirements for heavy metals, microbial content, and processing residues. For a product applied to skin, we consider this the right benchmark. It's also hexane-free, meaning the seeds were cold-pressed mechanically rather than solvent-extracted, which preserves the oil's natural profile and avoids residual chemical contamination.
In our products
You'll find castor oil in all of our cold-process soaps and body butters, where it works quietly in the background, never the dominant ingredient, always making the formula better. It's one of those ingredients that's easy to overlook on a label but impossible to remove without noticing.
