DIY Natural Soap Recipe: A Safe, Simple Cold-Process Guide

This recipe favors a mild, stable bar with easy trace and a creamy lather. Follow the grams, keep it cool and calm, and you’ll get consistent results.

Background & common pitfalls

Traditional bar soap is the sodium salts of fatty acids formed when triglyceride oils react with sodium hydroxide (lye). That reaction is saponification Journal of Chemical Education – pubs.acs.org, MDPI review via PubMed Central – nih.gov. Products with synthetic surfactants are legally cosmetics/detergents, not true soap, per FDA definitions FDA guidance – fda.gov, FDA FAQ – fda.gov. Lye is strongly caustic; NIOSH lists eye/skin burns and prescribes splash protection and quick-drench access NIOSH Pocket Guide – cdc.gov.

“Cold saponification uses the heat generated by combining fatty acids with sodium hydroxide; the mixture is then poured to finish saponifying and cure.” — N. P. Vidal, cosmetic chemistry researcher PubMed Central – nih.gov

Statistic to know: Healthy skin’s surface is mildly acidic, averaging about pH 4.7 in large human datasets. High-pH cleansers can raise skin pH transiently before it returns to baseline International Journal of Cosmetic Science (PubMed) – pubmed.ncbi.nlm.nih.gov, Role of pH in diagnosis – nih.gov.

A reliable cold-process recipe (small batch)

Target: ~1 kg batter, unscented and gentle. Superfat ~5%.

• Olive oil: 450 g
• Coconut oil (76): 250 g
• Shea butter: 150 g
• Castor oil: 50 g
• Distilled water: 300 g
• Sodium hydroxide (NaOH) beads/flakes: 133 g

Why these? Olive brings mildness, coconut adds cleansing/lather, shea contributes conditioning, castor stabilizes bubbles. The water and NaOH are calibrated to these oils and superfat. If you swap oils, recalculate lye in a reputable lye calculator.

Step-by-step (read fully before starting)

1) Gear & safety setup

• Goggles, gloves, long sleeves; tie back hair.
• Scale accurate to 1 g, stick blender, heat-safe pitcher for lye, non-reactive pot for oils, silicone mold, thermometer, parchment, vinegar for neutralizing surfaces (not skin).
• Ventilation: open window or fan. Keep pets/kids away. Lye is caustic; follow NIOSH cautions NIOSH – cdc.gov.

2) Make the lye solution

• Weigh 300 g distilled water in a heat-safe container.
• Slowly add lye to water (never water into lye), stirring until dissolved. Fumes are brief; avoid inhalation. Solution heats quickly and clears as crystals dissolve NIOSH – cdc.gov.
• Set aside to cool until warm to the touch.

3) Melt oils and combine

• Melt coconut oil and shea just until liquefied; add olive and castor.
• When oils and lye are both comfortably warm (not hot), pour lye solution into oils.
• Stick-blend in short pulses until “light trace” (thin custard texture).

4) Pour, insulate, unmold, cure

• Pour into a lined or silicone mold. Tap to release bubbles.
• Cover lightly for the first period so heat doesn’t escape too fast.
• Unmold and cut once firm. Space bars for airflow and let them cure on a rack until hard and mild. Curing allows water to evaporate and the last saponification to finish Cold saponification review – nih.gov.

Add-ins (optional)

• Essential oils: Many people use low percentages and avoid known sensitizers. If you add fragrance, research dermal limits from reputable safety sheets.
• Clays, botanicals, oats: Pre-disperse in a bit of oil or water and add at light trace.

Tips & common mistakes

• Don’t guess lye: Always run a fresh lye calculation if you change oils or batch size.
• Don’t rush pour: Over-blending can seize batter. Pulse and stir.
• Do label and store safely: Keep lye labeled and dry; never in food containers.

Key terms

• Saponification: Base-catalyzed hydrolysis of triglycerides to soap and glycerol.
• Superfat: A small portion of oils left unsaponified for mildness.
• Trace: The point at which emulsified batter leaves faint trails on the surface.

FAQ

What pH should finished bar soap have?

Handmade bars are typically alkaline. Skin’s natural surface pH averages about 4.7, so any bar will raise it temporarily; it generally settles back after rinsing and time PubMed – Skin pH, NIH – pH & diagnostics.

Is “natural soap” the same as a syndet bar?

No. If the cleaning comes from synthetic surfactants, it’s not “soap” under FDA’s definition, even if the label uses the word FDA – Is it a cosmetic, a drug, or soap?, FDA FAQ.

Can I make soap without lye?

You can melt-and-pour a pre-saponified base. All true bar soap is made with lye at some stage; otherwise it’s a detergent bar FDA FAQ.

Safety

• Lye handling: Wear goggles and gloves; add lye to water; work with ventilation; keep an eyewash path clear. NIOSH lists burns and mandates splash protection and quick-drench capability for sodium hydroxide NIOSH Pocket Guide – cdc.gov.
• Skin considerations: Because skin averages ~pH 4.7, some people prefer limiting bar use on the face and following with a gentle rinse and moisturizer, especially if sensitive PubMed – skin pH, NIH – pH & diagnostics.
• Regulatory note: Avoid drug-like claims (e.g., “treats eczema”). That can move your product under different rules FDA authority over cosmetics – fda.gov.
• Who should avoid: People with known fragrance allergies, open skin conditions, or severe eczema should consider patch testing or using fragrance-free products. Keep all soap and lye out of reach of children and pets.

Sources

• Is it a cosmetic, a drug, or soap? – U.S. FDA
• FAQ on Soap – U.S. FDA
• Sodium hydroxide safety – NIOSH Pocket Guide (CDC)
• Soapmaking chemistry – Journal of Chemical Education (ACS Publications)
• Cold saponification overview – MDPI via PubMed Central
• Average skin surface pH ≈ 4.7 – International Journal of Cosmetic Science (PubMed)

Conclusion

Soap is chemistry you can do at home safely: measure in grams, respect lye, keep the batter cool and even, and let the bars cure. Start with a simple base formula, then tweak oils, colors, and scents once you’re comfortable.