Many cosmetic products behave like structured materials when they are at rest. They can remain inside a jar or tube without flowing under their own weight.

When sufficient force is applied, the internal structure begins to break down and the material starts to flow. The stress required to initiate this process is called yield stress.

Cosmetic Importance

Yield stress influences whether a cream stays on a vertical surface, how easily a product can be squeezed from a tube and how a gel behaves when dispensed.

A higher yield stress can produce a more structured product, while a lower yield stress can create easier dispensing and spreading.

Measurement

Yield stress can be measured using rheological methods. The exact value depends on the measurement method and should therefore always be reported together with the test conditions.

References

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

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

ISO 3219-1. Rheology — Part 1: General principles and rheometry.

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