Compatibility and Preservation of Shampoo Formulation using SweetWash™ Hair Base and Cationic Collagen

Question

I am planning to formulate a shampoo using SweetWash™ Hair as a foaming base, adding Hair Collagen (Laurdimonium Hydroxypropyl Hydrolyzed Collagen) and Hydrolyzed Silk Protein. I have two technical concerns regarding this formulation: Compatibility: The Cationic Collagen is specified as incompatible with anionic surfactants. The SweetWash™ Hair base contains Sodium Xylenesulfonate (an anionic hydrotrope). Even with a 1:1 water dilution, will this combination cause precipitation, loss of viscosity, or inactivation of the collagen’s cationic charge? Can the Cocamidopropyl Hydroxysultaine (amphoteric) in the base prevent complex formation between the anionic and cationic components? Preservation: The base contains Phenoxyethanol and Chlorphenesin. However, I plan to dilute the base with 50% water and add 2% natural proteins (Silk and Collagen). Is the existing preservative system sufficient for this high water and protein load, or should I add a broad-spectrum preservative like Saliguard AZ or extra Phenoxyethanol?

MySkinRecipes Expert · Accepted Answer

Regarding your shampoo formulation using SweetWash™ Hair as a base, here are the technical considerations for your two questions:

1. Compatibility: Cationic Collagen vs. Anionic Components

The Hair Collagen (Laurdimonium Hydroxypropyl Hydrolyzed Collagen) is a cationic (positively charged) ingredient. While the SweetWash™ Hair base contains Sodium Xylene Sulfonate (an anionic hydrotrope), the primary surfactants in this base are Coco Glucoside (non-ionic) and Cocamidopropyl Hydroxysultaine (amphoteric).

Complex Formation: In many cases, amphoteric surfactants like Cocamidopropyl Hydroxysultaine act as a "bridge" to help stabilize cationic ingredients in the presence of anionic ones. However, because the collagen specifically warns against anionic detergents, there is a risk of forming a "coacervate" (a cloudy complex).
Viscosity & Stability: At a 1:1 dilution, the system is less concentrated, which may reduce the immediate risk of heavy precipitation, but it could still lead to a loss of clarity or a change in viscosity over time.
Recommendation: We strongly recommend performing a small "jar test" (mixing a small sample) first. If the mixture remains clear and stable after 24-48 hours, it is compatible. If it turns very cloudy or separates, you may need to replace the cationic collagen with a non-ionic protein like Hydrolyzed Silk Protein or Hydrolyzed Plant Keratin.

2. Preservation: Dilution and Protein Load

The built-in preservative system in SweetWash™ Hair (Phenoxyethanol and Chlorphenesin) is designed to protect the concentrated base.

Dilution Risk: When you dilute the base with 50% water, you are effectively cutting the preservative concentration in half.
Protein Load: Adding 2% natural proteins (Silk and Collagen) significantly increases the risk of microbial growth, as proteins serve as a nutrient source for bacteria and fungi.
Recommendation: It is highly recommended to add an additional broad-spectrum preservative. Adding 0.5-1.0% of a preservative like Phenoxyethanol or a broad-spectrum system (such as those in the Saliguard range) will ensure the long-term stability and safety of your diluted, protein-rich formula.