Suspensions
What Are Suspensions?
Suspensions are formulations in which insoluble particles, such as active ingredients or functional excipients, are dispersed in a liquid or semisolid medium that acts as the vehicle.
They can be used for topical application and to deliver substances to the skin. Common cosmetic examples include sun-protection products and pearlescent nail lacquers containing pigments.
Stability of Suspensions
Because suspended particles may have a different density from the surrounding vehicle, sedimentation can occur during storage. To ensure a homogeneous product during application, the particles should either remain sufficiently suspended or be readily redispersible by shaking before use.
Sedimentation can be reduced by:
- Reducing particle size
- Increasing the viscosity of the vehicle
- Developing a thixotropic system
The formulation should be designed so that any settled particles can be easily redispersed and the product provides a consistent application.
The Role of the Vehicle
The liquid or semisolid phase determines many of the application properties of a suspension. Its effect on the skin is comparable to the vehicle phase in other cosmetic formulations, such as solutions and emulsions.
References
Handbook of Cosmetic Science and Technology – André O. Barel, Marc Paye, Howard I. Maibach.
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