Understanding Caprylhydroxamic Acid Solubility in Serums

It is normal for Caprylhydroxamic Acid to precipitate as white flakes when mixed with Butylene Glycol and water, especially in a very liquid serum formulation. Here's why:

• Solubility: Caprylhydroxamic Acid has limited solubility in water (less than 0.14%) but is soluble in glycols like Butylene Glycol. However, in a serum that is primarily water, the overall solubility of Caprylhydroxamic Acid in the final mixture is restricted by the high water content.
• Temperature Effect: Heating the mixture increases the solubility, allowing the Caprylhydroxamic Acid to dissolve. But as the solution cools back down, the solubility decreases, causing the excess amount to crystallize out and form flakes again.

While Caprylhydroxamic Acid can be used in serums, its low water solubility makes it challenging to incorporate smoothly into very liquid, water-based formulations without precipitation issues, particularly at higher concentrations within the recommended usage rate (0.1-0.5%). It might be easier to incorporate into formulations with a higher oil or glycol phase, or thicker bases like creams and gels where the structure can help suspend particles even if not fully dissolved.

For easier use in liquid formulations, it is often recommended to use a pre-mixed liquid preservative blend that contains Caprylhydroxamic Acid, such as Spectrastat BHL or Spectrastat PHL, as these are formulated for better solubility and ease of use in liquid systems.