A thixotropic material becomes easier to flow when it is subjected to shear for a period of time. When the shear is removed, its internal structure gradually rebuilds and viscosity increases again.

This behavior is common in many structured cosmetic systems.

Cosmetic Applications

Thixotropy can be desirable because a product may remain relatively thick and stable in its container but become easier to dispense and spread during application.

For example, a cream can have sufficient structure to remain stable on a shelf while becoming more fluid when rubbed onto the skin.

Formulation Considerations

The rate of structural breakdown and recovery is important. If recovery is too slow, the product may remain excessively fluid after application. If recovery is very fast, the product may feel difficult to spread.

Thixotropy should be distinguished from simple shear-thinning behavior because thixotropy specifically involves a time-dependent structural change.

References

Barnes, H. A. A Handbook of Elementary Rheology.

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

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