The aqueous phase is the water-rich part of a cosmetic formulation. In conventional emulsions, it is combined with an oil phase to produce the final emulsion.

Purified water is usually the major component, but the aqueous phase may also contain glycerin, propanediol, glycols, water-soluble polymers, acids, bases, buffers, chelating agents, preservatives and water-soluble active ingredients.

The composition of the aqueous phase has a major influence on the final properties of the formulation. pH, conductivity, ionic strength and dissolved solids can affect viscosity, emulsification, preservation and ingredient stability.

Processing

The order of addition can be particularly important. Some polymers need to be fully hydrated before electrolytes are introduced, while certain active ingredients should only be added during the cooling phase because they are heat sensitive.

Water quality is also critical. Variations in mineral content, microbial quality and conductivity can contribute to differences between batches.

Formulation Considerations

The aqueous phase should be evaluated for pH, clarity, viscosity and compatibility before and after incorporation into the complete formulation.

Changes in the aqueous phase can influence the performance of emulsifiers, preservatives and rheology modifiers, meaning that an ingredient that behaves well in water alone may behave differently in the finished product.

References

Barel, A. O., Paye, M. and Maibach, H. I. Handbook of Cosmetic Science and Technology. CRC Press.

European Commission. CosIng – Cosmetic Ingredients Database.

Lachman, L., Lieberman, H. A. and Kanig, J. L. The Theory and Practice of Industrial Pharmacy.

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