What Is Castile Soap? A Beginner's Guide

Castile soap takes its name from the Castile region of Spain, where soap makers traditionally used olive oil instead of animal fats. Today the name describes any soap made purely from vegetable oils.

How liquid castile soap is made

Plant oils are combined with potassium hydroxide in a process called saponification. The oils turn into soap and glycerine. Using potassium (rather than sodium, which makes bar soap) gives a soap that stays liquid.

What makes it different?

• Plant-based: no animal fats.
• SLS-free: it is a true soap rather than a synthetic detergent.
• Concentrated: a small amount, diluted with water, goes a long way.
• Versatile: one bottle can replace several single-use cleaning products.
• Biodegradable: plant-oil soaps break down readily.

What can you use it for?

• Hand soap and foaming hand wash
• Body wash
• Washing-up liquid for dishes
• Multi-surface spray
• Floor cleaning
• Laundry and hand-washing delicates
• Cleaning fruit and vegetables (rinse well)
• Pet bathing (rinse thoroughly)

Tips for first-time users

• Always dilute. Neat castile is very concentrated. See our castile dilution guide for exact ratios.
• Use soft or distilled water in hard water areas. Minerals react with soap and can leave a film.
• Do not mix with vinegar or lemon juice. Acids turn the soap back into oils and leave a greasy residue.
• Avoid contact with eyes. It stings like any soap.

How long does it last?

Undiluted castile soap keeps well when the cap is closed. Diluted mixes are best made in small batches and used within a few weeks.

Shop: Organic Castile Liquid Soap, unscented and SLS-free.