What actually goes into a shampoo?
Short answer
A shampoo is five systems working together: a primary surfactant for cleaning, a secondary surfactant to soften it, cationic conditioning agents, pH and rheology modifiers, and a broad-spectrum preservative.
Explanation
The book treats a modern shampoo as an engineered system rather than a recipe, and names five ingredient classes.
Primary surfactants — anionic surfactants such as Sodium Laureth Sulfate (SLES) or the milder Sodium Cocoyl Isethionate (SCI) — do the cleaning. Their molecules surround oil and grease so it can be suspended in water and rinsed away. Secondary or co-surfactants such as Cocamidopropyl Betaine (CAPB) or Decyl Glucoside are added to modify the primary: they improve foam quality and stability, reduce irritation potential and can add viscosity.
Conditioning and stabilizing agents — cationic polymers such as Polyquaternium-10, proteins and silicones — deposit on the hair shaft after cleansing, neutralize static charge, smooth the cuticle and improve manageability. In solid formats an emulsifier like BTMS is essential to bind the oil and water phases.
pH and rheology modifiers set the rest. A shampoo should be slightly acidic, pH 4.5–5.5, to match hair's natural state and help close the cuticle; citric or lactic acid adjusts it. Xanthan gum or a salt such as sodium chloride controls flow and thickness.
Finally, preservation is non-negotiable. Anything containing water supports microbial growth, so a broad-spectrum system — a phenoxyethanol-based blend, or potassium sorbate with sodium benzoate — is required for safety and shelf life.
What to do
- Pick the primary surfactant first, then choose a co-surfactant to soften it.
- Add cationic conditioners after the surfactants, not with them.
- Adjust pH to 4.5–5.5 as the last step before the preservative.
Source: The Big Book of Homemade Hair Care — The Shampoo Matrix: Beyond Basic Cleansing