Water solubility influences whether an ingredient can be incorporated directly into the aqueous phase or requires another formulation strategy.

Many ingredients are highly water soluble, while others are only slightly soluble or practically insoluble.

The solubility of ionizable ingredients can change dramatically with pH.

pH Dependence

Weak acids and bases may become substantially more soluble when converted into their ionized forms. However, changing the pH can simultaneously affect skin compatibility, preservative performance or the stability of other ingredients.

Formulation Considerations

Poor water solubility may lead to precipitation, crystallization or loss of uniformity.

Possible approaches include co-solvents, solubilizers, emulsification, encapsulation or changing the chemical form of the ingredient where appropriate.

References

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

European Commission. CosIng – Cosmetic Ingredients Database.

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