Beginner Guide to Surfactant Formulation
How surfactants work, the four charge types, and how to build a basic cleanser
Surfactants are the functional core of every shampoo, body wash, face wash, hand soap, and cleansing bar. Understanding how they work and how to combine them effectively is foundational to formulating any cleansing product. The good news: surfactant formulation follows clear rules, and once you understand charge compatibility and ASM targets, building a stable cleanser becomes straightforward.
How surfactants clean
A surfactant molecule has a hydrophilic (water-loving) head and a hydrophobic (oil-loving) tail. In water, surfactant molecules arrange themselves into spherical structures called micelles — their tails pointing inward toward a trapped pocket of oil, and their heads facing outward into the water. The micelle forms around a droplet of oil, grease, or sebum, and the whole structure can be rinsed away.
Why you need to lather and rinse
The four surfactant charge types
| Charge type | Charge | Role | Common examples |
|---|---|---|---|
| Anionic | Negative | Primary cleansing; produces most foam | SLES, SLS, SCI, SLSA, sodium cocoyl glutamate |
| Cationic | Positive | Conditioning; not compatible with anionic primary cleansers | Behentrimonium chloride, cetrimonium chloride, BTMS |
| Amphoteric / zwitterionic | Both + and − | Secondary surfactant; boosts foam; reduces anionic harshness; bridges charges | Cocamidopropyl betaine, sodium cocoamphoacetate |
| Nonionic | None | Boosts mildness; thickens; stabilizes foam; pH-insensitive | Decyl glucoside, coco glucoside, PEG-40 hydrogenated castor oil |
Charge compatibility rules
Building a basic cleanser — the blend approach
Most cleansers use a primary surfactant plus one or two secondary surfactants to improve mildness, boost foam, or improve feel. A simple starting framework:
| Component | Typical % | Role |
|---|---|---|
| Primary anionic surfactant (SLES or sodium cocoyl glutamate) | 30–45% | Main cleansing and foam base |
| Amphoteric co-surfactant (cocamidopropyl betaine) | 10–20% | Foam booster; mildness enhancer; viscosity with SLES |
| Nonionic co-surfactant (decyl glucoside) | 5–15% | Mildness; adds gentleness for sensitive skin claims |
| Humectant (glycerin) | 2–5% | Skin feel; reduces post-wash tightness |
| Preservative | Per manufacturer rate | Required — water-based formula |
| Fragrance or EO | 0.5–1% | Optional |
| Distilled water | To 100% | Base |
Note on surfactant solution percentages
Pro Tip
pH of surfactant formulas
Most surfactant formulas are adjusted to a skin-compatible pH of 4.5–6.5. SLES and many anionic surfactants are stable across this range. Glucoside surfactants (decyl glucoside, coco glucoside) often run alkaline from manufacture — you may need to adjust pH down with citric acid solution. Always check and adjust pH before packaging.
- Measure pH with a calibrated pH meter — strips are not accurate enough in surfactant solutions.
- To lower pH: dilute citric acid (10–20% solution) — add dropwise, mix, measure, repeat.
- To raise pH: dilute sodium hydroxide or triethanolamine (TEA) solution — add very carefully.
- Target pH 4.5–6 for scalp/skin; 5.5–6.5 for gentler formulas.